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postgres/doc/src/sgml/func.sgml
Tom Lane d28cd2273b Improve description of geometric operators.
2003-03-03 03:31:23 +00:00

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<!--
$Header: /cvsroot/pgsql/doc/src/sgml/func.sgml,v 1.142 2003/03/03 03:31:23 tgl Exp $
PostgreSQL documentation
-->
<chapter id="functions">
<title>Functions and Operators</title>
<indexterm zone="functions">
<primary>functions</primary>
</indexterm>
<indexterm zone="functions">
<primary>operators</primary>
</indexterm>
<para>
<productname>PostgreSQL</productname> provides a large number of
functions and operators for the built-in data types. Users can also
define their own functions and operators, as described in the
&cite-programmer;. The
<application>psql</application> commands <command>\df</command> and
<command>\do</command> can be used to show the list of all actually
available functions and operators, respectively.
</para>
<para>
If you are concerned about portability then take note that most of
the functions and operators described in this chapter, with the
exception of the most trivial arithmetic and comparison operators
and some explicitly marked functions, are not specified by the
<acronym>SQL</acronym>
standard. Some of this extended functionality is present in other
<acronym>SQL</acronym> implementations, and in many cases this
functionality is compatible and consistent between various products.
</para>
<sect1 id="functions-logical">
<title>Logical Operators</title>
<indexterm zone="functions-logical">
<primary>operators</primary>
<secondary>logical</secondary>
</indexterm>
<indexterm>
<primary>Boolean</primary>
<secondary>operators</secondary>
<see>operators, logical</see>
</indexterm>
<para>
The usual logical operators are available:
<indexterm>
<primary>and</primary>
<secondary>operator</secondary>
</indexterm>
<indexterm>
<primary>or</primary>
<secondary>operator</secondary>
</indexterm>
<indexterm>
<primary>not</primary>
<secondary>operator</secondary>
</indexterm>
<simplelist>
<member>AND</member>
<member>OR</member>
<member>NOT</member>
</simplelist>
<acronym>SQL</acronym> uses a three-valued Boolean logic where the null value represents
<quote>unknown</quote>. Observe the following truth tables:
<informaltable>
<tgroup cols="4">
<thead>
<row>
<entry><replaceable>a</replaceable></entry>
<entry><replaceable>b</replaceable></entry>
<entry><replaceable>a</replaceable> AND <replaceable>b</replaceable></entry>
<entry><replaceable>a</replaceable> OR <replaceable>b</replaceable></entry>
</row>
</thead>
<tbody>
<row>
<entry>TRUE</entry>
<entry>TRUE</entry>
<entry>TRUE</entry>
<entry>TRUE</entry>
</row>
<row>
<entry>TRUE</entry>
<entry>FALSE</entry>
<entry>FALSE</entry>
<entry>TRUE</entry>
</row>
<row>
<entry>TRUE</entry>
<entry>NULL</entry>
<entry>NULL</entry>
<entry>TRUE</entry>
</row>
<row>
<entry>FALSE</entry>
<entry>FALSE</entry>
<entry>FALSE</entry>
<entry>FALSE</entry>
</row>
<row>
<entry>FALSE</entry>
<entry>NULL</entry>
<entry>FALSE</entry>
<entry>NULL</entry>
</row>
<row>
<entry>NULL</entry>
<entry>NULL</entry>
<entry>NULL</entry>
<entry>NULL</entry>
</row>
</tbody>
</tgroup>
</informaltable>
<informaltable>
<tgroup cols="2">
<thead>
<row>
<entry><replaceable>a</replaceable></entry>
<entry>NOT <replaceable>a</replaceable></entry>
</row>
</thead>
<tbody>
<row>
<entry>TRUE</entry>
<entry>FALSE</entry>
</row>
<row>
<entry>FALSE</entry>
<entry>TRUE</entry>
</row>
<row>
<entry>NULL</entry>
<entry>NULL</entry>
</row>
</tbody>
</tgroup>
</informaltable>
</para>
</sect1>
<sect1 id="functions-comparison">
<title>Comparison Operators</title>
<indexterm zone="functions-comparison">
<primary>comparison</primary>
<secondary>operators</secondary>
</indexterm>
<para>
The usual comparison operators are available, shown in <xref
linkend="functions-comparison-table">.
</para>
<table id="functions-comparison-table">
<title>Comparison Operators</title>
<tgroup cols="2">
<thead>
<row>
<entry>Operator</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry> <literal>&lt;</literal> </entry>
<entry>less than</entry>
</row>
<row>
<entry> <literal>&gt;</literal> </entry>
<entry>greater than</entry>
</row>
<row>
<entry> <literal>&lt;=</literal> </entry>
<entry>less than or equal to</entry>
</row>
<row>
<entry> <literal>&gt;=</literal> </entry>
<entry>greater than or equal to</entry>
</row>
<row>
<entry> <literal>=</literal> </entry>
<entry>equal</entry>
</row>
<row>
<entry> <literal>&lt;&gt;</literal> or <literal>!=</literal> </entry>
<entry>not equal</entry>
</row>
</tbody>
</tgroup>
</table>
<note>
<para>
The <literal>!=</literal> operator is converted to
<literal>&lt;&gt;</literal> in the parser stage. It is not
possible to implement <literal>!=</literal> and
<literal>&lt;&gt;</literal> operators that do different things.
</para>
</note>
<para>
Comparison operators are available for all data types where this
makes sense. All comparison operators are binary operators that
return values of type <type>boolean</type>; expressions like
<literal>1 &lt; 2 &lt; 3</literal> are not valid (because there is
no <literal>&lt;</literal> operator to compare a Boolean value with
<literal>3</literal>).
</para>
<para>
<indexterm>
<primary>between</primary>
</indexterm>
In addition to the comparison operators, the special
<token>BETWEEN</token> construct is available.
<synopsis>
<replaceable>a</replaceable> BETWEEN <replaceable>x</replaceable> AND <replaceable>y</replaceable>
</synopsis>
is equivalent to
<synopsis>
<replaceable>a</replaceable> &gt;= <replaceable>x</replaceable> AND <replaceable>a</replaceable> &lt;= <replaceable>y</replaceable>
</synopsis>
Similarly,
<synopsis>
<replaceable>a</replaceable> NOT BETWEEN <replaceable>x</replaceable> AND <replaceable>y</replaceable>
</synopsis>
is equivalent to
<synopsis>
<replaceable>a</replaceable> &lt; <replaceable>x</replaceable> OR <replaceable>a</replaceable> &gt; <replaceable>y</replaceable>
</synopsis>
There is no difference between the two respective forms apart from
the <acronym>CPU</acronym> cycles required to rewrite the first one
into the second one internally.
</para>
<para>
To check whether a value is or is not null, use the constructs
<synopsis>
<replaceable>expression</replaceable> IS NULL
<replaceable>expression</replaceable> IS NOT NULL
</synopsis>
or the equivalent, but nonstandard, constructs
<synopsis>
<replaceable>expression</replaceable> ISNULL
<replaceable>expression</replaceable> NOTNULL
</synopsis>
</para>
<para>
Do <emphasis>not</emphasis> write
<literal><replaceable>expression</replaceable> = NULL</literal>
because <literal>NULL</> is not <quote>equal to</quote>
<literal>NULL</>. (The null value represents an unknown value,
and it is not known whether two unknown values are equal.)
</para>
<para>
Some applications may (incorrectly) require that
<literal><replaceable>expression</replaceable> = NULL</literal>
returns true if <replaceable>expression</replaceable> evaluates to
the null value. To support these applications, the run-time option
<varname>transform_null_equals</varname> can be turned on (e.g.,
<literal>SET transform_null_equals TO ON;</literal>).
<productname>PostgreSQL</productname> will then convert
<literal>x = NULL</literal> clauses to
<literal>x IS NULL</literal>. This was
the default behavior in releases 6.5 through 7.1.
</para>
<para>
Boolean values can also be tested using the constructs
<synopsis>
<replaceable>expression</replaceable> IS TRUE
<replaceable>expression</replaceable> IS NOT TRUE
<replaceable>expression</replaceable> IS FALSE
<replaceable>expression</replaceable> IS NOT FALSE
<replaceable>expression</replaceable> IS UNKNOWN
<replaceable>expression</replaceable> IS NOT UNKNOWN
</synopsis>
These are similar to <literal>IS NULL</literal> in that they will
always return true or false, never a null value, even when the operand is null.
A null input is treated as the logical value <quote>unknown</>.
</para>
</sect1>
<sect1 id="functions-math">
<title>Mathematical Functions and Operators</title>
<para>
Mathematical operators are provided for many
<productname>PostgreSQL</productname> types. For types without
common mathematical conventions for all possible permutations
(e.g., date/time types) we
describe the actual behavior in subsequent sections.
</para>
<para>
<xref linkend="functions-math-op-table"> shows the available mathematical operators.
</para>
<table id="functions-math-op-table">
<title>Mathematical Operators</title>
<tgroup cols="4">
<thead>
<row>
<entry>Name</entry>
<entry>Description</entry>
<entry>Example</entry>
<entry>Result</entry>
</row>
</thead>
<tbody>
<row>
<entry> <literal>+</literal> </entry>
<entry>addition</entry>
<entry>2 + 3</entry>
<entry>5</entry>
</row>
<row>
<entry> <literal>-</literal> </entry>
<entry>subtraction</entry>
<entry>2 - 3</entry>
<entry>-1</entry>
</row>
<row>
<entry> <literal>*</literal> </entry>
<entry>multiplication</entry>
<entry>2 * 3</entry>
<entry>6</entry>
</row>
<row>
<entry> <literal>/</literal> </entry>
<entry>division (integer division truncates results)</entry>
<entry>4 / 2</entry>
<entry>2</entry>
</row>
<row>
<entry> <literal>%</literal> </entry>
<entry>modulo (remainder)</entry>
<entry>5 % 4</entry>
<entry>1</entry>
</row>
<row>
<entry> <literal>^</literal> </entry>
<entry>exponentiation</entry>
<entry>2.0 ^ 3.0</entry>
<entry>8</entry>
</row>
<row>
<entry> <literal>|/</literal> </entry>
<entry>square root</entry>
<entry>|/ 25.0</entry>
<entry>5</entry>
</row>
<row>
<entry> <literal>||/</literal> </entry>
<entry>cube root</entry>
<entry>||/ 27.0</entry>
<entry>3</entry>
</row>
<row>
<entry> <literal>!</literal> </entry>
<entry>factorial</entry>
<entry>5 !</entry>
<entry>120</entry>
</row>
<row>
<entry> <literal>!!</literal> </entry>
<entry>factorial (prefix operator)</entry>
<entry>!! 5</entry>
<entry>120</entry>
</row>
<row>
<entry> <literal>@</literal> </entry>
<entry>absolute value</entry>
<entry>@ -5.0</entry>
<entry>5</entry>
</row>
<row>
<entry> <literal>&amp;</literal> </entry>
<entry>binary AND</entry>
<entry>91 &amp; 15</entry>
<entry>11</entry>
</row>
<row>
<entry> <literal>|</literal> </entry>
<entry>binary OR</entry>
<entry>32 | 3</entry>
<entry>35</entry>
</row>
<row>
<entry> <literal>#</literal> </entry>
<entry>binary XOR</entry>
<entry>17 # 5</entry>
<entry>20</entry>
</row>
<row>
<entry> <literal>~</literal> </entry>
<entry>binary NOT</entry>
<entry>~1</entry>
<entry>-2</entry>
</row>
<row>
<entry> &lt;&lt; </entry>
<entry>binary shift left</entry>
<entry>1 &lt;&lt; 4</entry>
<entry>16</entry>
</row>
<row>
<entry> &gt;&gt; </entry>
<entry>binary shift right</entry>
<entry>8 &gt;&gt; 2</entry>
<entry>2</entry>
</row>
</tbody>
</tgroup>
</table>
<para>
The <quote>binary</quote> operators are also available for the bit
string types <type>BIT</type> and <type>BIT VARYING</type>, as
shown in <xref linkend="functions-math-bit-table">.
Bit string arguments to <literal>&amp;</literal>, <literal>|</literal>,
and <literal>#</literal> must be of equal length. When bit
shifting, the original length of the string is preserved, as shown
in the table.
</para>
<table id="functions-math-bit-table">
<title>Bit String Binary Operators</title>
<tgroup cols="2">
<thead>
<row>
<entry>Example</entry>
<entry>Result</entry>
</row>
</thead>
<tbody>
<row>
<entry>B'10001' &amp; B'01101'</entry>
<entry>00001</entry>
</row>
<row>
<entry>B'10001' | B'01101'</entry>
<entry>11101</entry>
</row>
<row>
<entry>B'10001' # B'01101'</entry>
<entry>11110</entry>
</row>
<row>
<entry>~ B'10001'</entry>
<entry>01110</entry>
</row>
<row>
<entry>B'10001' &lt;&lt; 3</entry>
<entry>01000</entry>
</row>
<row>
<entry>B'10001' &gt;&gt; 2</entry>
<entry>00100</entry>
</row>
</tbody>
</tgroup>
</table>
<para>
<xref linkend="functions-math-func-table"> shows the available
mathematical functions. In the table, <literal>dp</literal>
indicates <type>double precision</type>. Many of these functions
are provided in multiple forms with different argument types.
Except where noted, any given form of a function returns the same
datatype as its argument.
The functions working with <type>double precision</type> data are mostly
implemented on top of the host system's C library; accuracy and behavior in
boundary cases may therefore vary depending on the host system.
</para>
<table id="functions-math-func-table">
<title>Mathematical Functions</title>
<tgroup cols="5">
<thead>
<row>
<entry>Function</entry>
<entry>Return Type</entry>
<entry>Description</entry>
<entry>Example</entry>
<entry>Result</entry>
</row>
</thead>
<tbody>
<row>
<entry><function>abs</function>(<replaceable>x</replaceable>)</entry>
<entry>(same as <replaceable>x</>)</entry>
<entry>absolute value</entry>
<entry><literal>abs(-17.4)</literal></entry>
<entry>17.4</entry>
</row>
<row>
<entry><function>cbrt</function>(<type>dp</type>)</entry>
<entry><type>dp</type></entry>
<entry>cube root</entry>
<entry><literal>cbrt(27.0)</literal></entry>
<entry>3</entry>
</row>
<row>
<entry><function>ceil</function>(<type>dp</type> or <type>numeric</type>)</entry>
<entry>(same as input)</entry>
<entry>smallest integer not less than argument</entry>
<entry><literal>ceil(-42.8)</literal></entry>
<entry>-42</entry>
</row>
<row>
<entry><function>degrees</function>(<type>dp</type>)</entry>
<entry><type>dp</type></entry>
<entry>radians to degrees</entry>
<entry><literal>degrees(0.5)</literal></entry>
<entry>28.6478897565412</entry>
</row>
<row>
<entry><function>exp</function>(<type>dp</type> or <type>numeric</type>)</entry>
<entry>(same as input)</entry>
<entry>exponential</entry>
<entry><literal>exp(1.0)</literal></entry>
<entry>2.71828182845905</entry>
</row>
<row>
<entry><function>floor</function>(<type>dp</type> or <type>numeric</type>)</entry>
<entry>(same as input)</entry>
<entry>largest integer not greater than argument</entry>
<entry><literal>floor(-42.8)</literal></entry>
<entry>-43</entry>
</row>
<row>
<entry><function>ln</function>(<type>dp</type> or <type>numeric</type>)</entry>
<entry>(same as input)</entry>
<entry>natural logarithm</entry>
<entry><literal>ln(2.0)</literal></entry>
<entry>0.693147180559945</entry>
</row>
<row>
<entry><function>log</function>(<type>dp</type> or <type>numeric</type>)</entry>
<entry>(same as input)</entry>
<entry>base 10 logarithm</entry>
<entry><literal>log(100.0)</literal></entry>
<entry>2</entry>
</row>
<row>
<entry><function>log</function>(<parameter>b</parameter> <type>numeric</type>,
<parameter>x</parameter> <type>numeric</type>)</entry>
<entry><type>numeric</type></entry>
<entry>logarithm to base <parameter>b</parameter></entry>
<entry><literal>log(2.0, 64.0)</literal></entry>
<entry>6.0000000000</entry>
</row>
<row>
<entry><function>mod</function>(<parameter>y</parameter>,
<parameter>x</parameter>)</entry>
<entry>(same as argument types)</entry>
<entry>remainder of <parameter>y</parameter>/<parameter>x</parameter></entry>
<entry><literal>mod(9,4)</literal></entry>
<entry>1</entry>
</row>
<row>
<entry><function>pi</function>()</entry>
<entry><type>dp</type></entry>
<entry><quote>Pi</quote> constant</entry>
<entry><literal>pi()</literal></entry>
<entry>3.14159265358979</entry>
</row>
<row>
<entry><function>pow</function>(<parameter>x</parameter> <type>dp</type>,
<parameter>e</parameter> <type>dp</type>)</entry>
<entry><type>dp</type></entry>
<entry>raise a number to exponent <parameter>e</parameter></entry>
<entry><literal>pow(9.0, 3.0)</literal></entry>
<entry>729</entry>
</row>
<row>
<entry><function>pow</function>(<parameter>x</parameter> <type>numeric</type>,
<parameter>e</parameter> <type>numeric</type>)</entry>
<entry><type>numeric</type></entry>
<entry>raise a number to exponent <parameter>e</parameter></entry>
<entry><literal>pow(9.0, 3.0)</literal></entry>
<entry>729</entry>
</row>
<row>
<entry><function>radians</function>(<type>dp</type>)</entry>
<entry><type>dp</type></entry>
<entry>degrees to radians</entry>
<entry><literal>radians(45.0)</literal></entry>
<entry>0.785398163397448</entry>
</row>
<row>
<entry><function>random</function>()</entry>
<entry><type>dp</type></entry>
<entry>random value between 0.0 and 1.0</entry>
<entry><literal>random()</literal></entry>
<entry></entry>
</row>
<row>
<entry><function>round</function>(<type>dp</type> or <type>numeric</type>)</entry>
<entry>(same as input)</entry>
<entry>round to nearest integer</entry>
<entry><literal>round(42.4)</literal></entry>
<entry>42</entry>
</row>
<row>
<entry><function>round</function>(<parameter>v</parameter> <type>numeric</type>, <parameter>s</parameter> <type>integer</type>)</entry>
<entry><type>numeric</type></entry>
<entry>round to <parameter>s</parameter> decimal places</entry>
<entry><literal>round(42.4382, 2)</literal></entry>
<entry>42.44</entry>
</row>
<row>
<entry><function>setseed</function>(<type>dp</type>)</entry>
<entry><type>int32</type></entry>
<entry>set seed for subsequent random() calls</entry>
<entry><literal>setseed(0.54823)</literal></entry>
<entry>1177314959</entry>
</row>
<row>
<entry><function>sign</function>(<type>dp</type> or <type>numeric</type>)</entry>
<entry>(same as input)</entry>
<entry>sign of the argument (-1, 0, +1)</entry>
<entry><literal>sign(-8.4)</literal></entry>
<entry>-1</entry>
</row>
<row>
<entry><function>sqrt</function>(<type>dp</type> or <type>numeric</type>)</entry>
<entry>(same as input)</entry>
<entry>square root</entry>
<entry><literal>sqrt(2.0)</literal></entry>
<entry>1.4142135623731</entry>
</row>
<row>
<entry><function>trunc</function>(<type>dp</type> or <type>numeric</type>)</entry>
<entry>(same as input)</entry>
<entry>truncate toward zero</entry>
<entry><literal>trunc(42.8)</literal></entry>
<entry>42</entry>
</row>
<row>
<entry><function>trunc</function>(<parameter>v</parameter> <type>numeric</type>, <parameter>s</parameter> <type>integer</type>)</entry>
<entry><type>numeric</type></entry>
<entry>truncate to <parameter>s</parameter> decimal places</entry>
<entry><literal>trunc(42.4382, 2)</literal></entry>
<entry>42.43</entry>
</row>
</tbody>
</tgroup>
</table>
<para>
Finally, <xref linkend="functions-math-trig-table"> shows the
available trigonometric functions. All trigonometric functions
take arguments and return values of type <type>double
precision</type>.
</para>
<table id="functions-math-trig-table">
<title>Trigonometric Functions</title>
<tgroup cols="2">
<thead>
<row>
<entry>Function</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry><function>acos</function>(<replaceable>x</replaceable>)</entry>
<entry>inverse cosine</entry>
</row>
<row>
<entry><function>asin</function>(<replaceable>x</replaceable>)</entry>
<entry>inverse sine</entry>
</row>
<row>
<entry><function>atan</function>(<replaceable>x</replaceable>)</entry>
<entry>inverse tangent</entry>
</row>
<row>
<entry><function>atan2</function>(<replaceable>x</replaceable>,
<replaceable>y</replaceable>)</entry>
<entry>inverse tangent of
<replaceable>x</replaceable>/<replaceable>y</replaceable></entry>
</row>
<row>
<entry><function>cos</function>(<replaceable>x</replaceable>)</entry>
<entry>cosine</entry>
</row>
<row>
<entry><function>cot</function>(<replaceable>x</replaceable>)</entry>
<entry>cotangent</entry>
</row>
<row>
<entry><function>sin</function>(<replaceable>x</replaceable>)</entry>
<entry>sine</entry>
</row>
<row>
<entry><function>tan</function>(<replaceable>x</replaceable>)</entry>
<entry>tangent</entry>
</row>
</tbody>
</tgroup>
</table>
</sect1>
<sect1 id="functions-string">
<title>String Functions and Operators</title>
<para>
This section describes functions and operators for examining and
manipulating string values. Strings in this context include values
of all the types <type>CHARACTER</type>, <type>CHARACTER
VARYING</type>, and <type>TEXT</type>. Unless otherwise noted, all
of the functions listed below work on all of these types, but be
wary of potential effects of the automatic padding when using the
<type>CHARACTER</type> type. Generally, the functions described
here also work on data of non-string types by converting that data
to a string representation first. Some functions also exist
natively for bit-string types.
</para>
<para>
<acronym>SQL</acronym> defines some string functions with a special syntax where
certain key words rather than commas are used to separate the
arguments. Details are in <xref linkend="functions-string-sql">.
These functions are also implemented using the regular syntax for
function invocation. (See <xref linkend="functions-string-other">.)
</para>
<table id="functions-string-sql">
<title><acronym>SQL</acronym> String Functions and Operators</title>
<tgroup cols="5">
<thead>
<row>
<entry>Function</entry>
<entry>Return Type</entry>
<entry>Description</entry>
<entry>Example</entry>
<entry>Result</entry>
</row>
</thead>
<tbody>
<row>
<entry> <parameter>string</parameter> <literal>||</literal>
<parameter>string</parameter> </entry>
<entry> <type>text</type> </entry>
<entry>
String concatenation
<indexterm>
<primary>character strings</primary>
<secondary>concatenation</secondary>
</indexterm>
</entry>
<entry><literal>'Post' || 'greSQL'</literal></entry>
<entry><literal>PostgreSQL</literal></entry>
</row>
<row>
<entry><function>bit_length</function>(<parameter>string</parameter>)</entry>
<entry><type>integer</type></entry>
<entry>Number of bits in string</entry>
<entry><literal>bit_length('jose')</literal></entry>
<entry><literal>32</literal></entry>
</row>
<row>
<entry><function>char_length</function>(<parameter>string</parameter>) or <function>character_length</function>(<parameter>string</parameter>)</entry>
<entry><type>integer</type></entry>
<entry>
Number of characters in string
<indexterm>
<primary>character strings</primary>
<secondary>length</secondary>
</indexterm>
<indexterm>
<primary>length</primary>
<secondary>character strings</secondary>
<see>character strings, length</see>
</indexterm>
</entry>
<entry><literal>char_length('jose')</literal></entry>
<entry><literal>4</literal></entry>
</row>
<row>
<entry><function>convert</function>(<parameter>string</parameter>
using <parameter>conversion_name</parameter>)</entry>
<entry><type>text</type></entry>
<entry>
Change encoding using specified conversion name. Conversions
can be defined by <command>CREATE CONVERSION</command>. Also
there are some pre-defined conversion names. See <xref
linkend="conversion-names"> for available conversion
names.
</entry>
<entry><literal>convert('PostgreSQL' using iso_8859_1_to_utf_8)</literal></entry>
<entry><literal>'PostgreSQL'</literal> in Unicode (UTF-8) encoding</entry>
</row>
<row>
<entry><function>lower</function>(<parameter>string</parameter>)</entry>
<entry><type>text</type></entry>
<entry>Convert string to lower case</entry>
<entry><literal>lower('TOM')</literal></entry>
<entry><literal>tom</literal></entry>
</row>
<row>
<entry><function>octet_length</function>(<parameter>string</parameter>)</entry>
<entry><type>integer</type></entry>
<entry>Number of bytes in string</entry>
<entry><literal>octet_length('jose')</literal></entry>
<entry><literal>4</literal></entry>
</row>
<row>
<entry><function>overlay</function>(<parameter>string</parameter> placing <parameter>string</parameter> from <type>integer</type> <optional>for <type>integer</type></optional>)</entry>
<entry><type>text</type></entry>
<entry>
Insert substring
<indexterm>
<primary>overlay</primary>
</indexterm>
</entry>
<entry><literal>overlay('Txxxxas' placing 'hom' from 2 for 4)</literal></entry>
<entry><literal>Thomas</literal></entry>
</row>
<row>
<entry><function>position</function>(<parameter>substring</parameter> in <parameter>string</parameter>)</entry>
<entry><type>integer</type></entry>
<entry>Location of specified substring</entry>
<entry><literal>position('om' in 'Thomas')</literal></entry>
<entry><literal>3</literal></entry>
</row>
<row>
<entry><function>substring</function>(<parameter>string</parameter> <optional>from <type>integer</type></optional> <optional>for <type>integer</type></optional>)</entry>
<entry><type>text</type></entry>
<entry>
Extract substring
<indexterm>
<primary>substring</primary>
</indexterm>
</entry>
<entry><literal>substring('Thomas' from 2 for 3)</literal></entry>
<entry><literal>hom</literal></entry>
</row>
<row>
<entry><function>substring</function>(<parameter>string</parameter> from <replaceable>pattern</replaceable>)</entry>
<entry><type>text</type></entry>
<entry>
Extract substring matching POSIX regular expression
<indexterm>
<primary>substring</primary>
</indexterm>
</entry>
<entry><literal>substring('Thomas' from '...$')</literal></entry>
<entry><literal>mas</literal></entry>
</row>
<row>
<entry><function>substring</function>(<parameter>string</parameter> from <replaceable>pattern</replaceable> for <replaceable>escape</replaceable>)</entry>
<entry><type>text</type></entry>
<entry>
Extract substring matching <acronym>SQL</acronym> regular
expression
<indexterm>
<primary>substring</primary>
</indexterm>
</entry>
<entry><literal>substring('Thomas' from '%#"o_a#"_' for '#')</literal></entry>
<entry><literal>oma</literal></entry>
</row>
<row>
<entry>
<function>trim</function>(<optional>leading | trailing | both</optional>
<optional><parameter>characters</parameter></optional> from
<parameter>string</parameter>)
</entry>
<entry><type>text</type></entry>
<entry>
Remove the longest string containing only the
<parameter>characters</parameter> (a space by default) from the
beginning/end/both ends of the <parameter>string</parameter>
</entry>
<entry><literal>trim(both 'x' from 'xTomxx')</literal></entry>
<entry><literal>Tom</literal></entry>
</row>
<row>
<entry><function>upper</function>(<parameter>string</parameter>)</entry>
<entry><type>text</type></entry>
<entry>Convert string to upper case</entry>
<entry><literal>upper('tom')</literal></entry>
<entry><literal>TOM</literal></entry>
</row>
</tbody>
</tgroup>
</table>
<para>
Additional string manipulation functions are available and are
listed in <xref linkend="functions-string-other">. Some of them are used internally to implement the
<acronym>SQL</acronym>-standard string functions listed in <xref linkend="functions-string-sql">.
</para>
<table id="functions-string-other">
<title>Other String Functions</title>
<tgroup cols="5">
<thead>
<row>
<entry>Function</entry>
<entry>Return Type</entry>
<entry>Description</entry>
<entry>Example</entry>
<entry>Result</entry>
</row>
</thead>
<tbody>
<row>
<entry><function>ascii</function>(<type>text</type>)</entry>
<entry>integer</entry>
<entry><acronym>ASCII</acronym> code of the first character of the argument.</entry>
<entry><literal>ascii('x')</literal></entry>
<entry><literal>120</literal></entry>
</row>
<row>
<entry><function>btrim</function>(<parameter>string</parameter> <type>text</type>, <parameter>trim</parameter> <type>text</type>)</entry>
<entry><type>text</type></entry>
<entry>
Remove (trim) the longest string consisting only of characters
in <parameter>trim</parameter> from the start and end of
<parameter>string</parameter>
</entry>
<entry><literal>btrim('xyxtrimyyx','xy')</literal></entry>
<entry><literal>trim</literal></entry>
</row>
<row>
<entry><function>chr</function>(<type>integer</type>)</entry>
<entry><type>text</type></entry>
<entry>Character with the given <acronym>ASCII</acronym> code</entry>
<entry><literal>chr(65)</literal></entry>
<entry><literal>A</literal></entry>
</row>
<row>
<entry>
<function>convert</function>(<parameter>string</parameter>
<type>text</type>,
<optional><parameter>src_encoding</parameter> <type>name</type>,</optional>
<parameter>dest_encoding</parameter> <type>name</type>)
</entry>
<entry><type>text</type></entry>
<entry>
Convert string to <parameter>dest_encoding</parameter>.
The original encoding is specified by
<parameter>src_encoding</parameter>. If
<parameter>src_encoding</parameter> is omitted, database
encoding is assumed.
</entry>
<entry><literal>convert('text_in_unicode', 'UNICODE', 'LATIN1')</literal></entry>
<entry><literal>text_in_unicode</literal> represented in ISO 8859-1</entry>
</row>
<row>
<entry>
<function>decode</function>(<parameter>string</parameter> <type>text</type>,
<parameter>type</parameter> <type>text</type>)
</entry>
<entry><type>bytea</type></entry>
<entry>
Decode binary data from <parameter>string</parameter> previously
encoded with <function>encode()</>. Parameter type is same as in <function>encode()</>.
</entry>
<entry><literal>decode('MTIzAAE=', 'base64')</literal></entry>
<entry><literal>123\000\001</literal></entry>
</row>
<row>
<entry>
<function>encode</function>(<parameter>data</parameter> <type>bytea</type>,
<parameter>type</parameter> <type>text</type>)
</entry>
<entry><type>text</type></entry>
<entry>
Encode binary data to <acronym>ASCII</acronym>-only representation. Supported
types are: base64, hex, escape.
</entry>
<entry><literal>encode('123\\000\\001', 'base64')</literal></entry>
<entry><literal>MTIzAAE=</literal></entry>
</row>
<row>
<entry><function>initcap</function>(<type>text</type>)</entry>
<entry><type>text</type></entry>
<entry>Convert first letter of each word (whitespace separated) to upper case</entry>
<entry><literal>initcap('hi thomas')</literal></entry>
<entry><literal>Hi Thomas</literal></entry>
</row>
<row>
<entry><function>length</function>(<parameter>string</parameter>)</entry>
<entry><type>integer</type></entry>
<entry>
Length of string
<indexterm>
<primary>character strings</primary>
<secondary>length</secondary>
</indexterm>
<indexterm>
<primary>length</primary>
<secondary>character strings</secondary>
<see>character strings, length</see>
</indexterm>
</entry>
<entry><literal>length('jose')</literal></entry>
<entry><literal>4</literal></entry>
</row>
<row>
<entry>
<function>lpad</function>(<parameter>string</parameter> <type>text</type>,
<parameter>length</parameter> <type>integer</type>
<optional>, <parameter>fill</parameter> <type>text</type></optional>)
</entry>
<entry>text</entry>
<entry>
Fill up the <parameter>string</parameter> to length
<parameter>length</parameter> by prepending the characters
<parameter>fill</parameter> (a space by default). If the
<parameter>string</parameter> is already longer than
<parameter>length</parameter> then it is truncated (on the
right).
</entry>
<entry><literal>lpad('hi', 5, 'xy')</literal></entry>
<entry><literal>xyxhi</literal></entry>
</row>
<row>
<entry><function>ltrim</function>(<parameter>string</parameter> <type>text</type>, <parameter>text</parameter> <type>text</type>)</entry>
<entry><type>text</type></entry>
<entry>
Remove the longest string containing only characters from
<parameter>trim</parameter> from the start of the string.
</entry>
<entry><literal>ltrim('zzzytrim','xyz')</literal></entry>
<entry><literal>trim</literal></entry>
</row>
<row>
<entry><function>md5</function>(<parameter>string</parameter> <type>text</type>)</entry>
<entry><type>text</type></entry>
<entry>
Calculates the MD5 hash of given string, returning the result in hex.
</entry>
<entry><literal>md5('abc')</literal></entry>
<entry><literal>900150983cd24fb0d6963f7d28e17f72</literal></entry>
</row>
<row>
<entry><function>pg_client_encoding</function>()</entry>
<entry><type>name</type></entry>
<entry>
Current client encoding name.
</entry>
<entry><literal>pg_client_encoding()</literal></entry>
<entry><literal>SQL_ASCII</literal></entry>
</row>
<row>
<entry><function>quote_ident</function>(<parameter>string</parameter> text)</entry>
<entry><type>text</type></entry>
<entry>
Return the given string suitably quoted to be used as an identifier
in an <acronym>SQL</acronym> query string.
Quotes are added only if necessary (i.e., if the string contains
non-identifier characters or would be case-folded).
Embedded quotes are properly doubled.
</entry>
<entry><literal>quote_ident('Foo')</literal></entry>
<entry><literal>"Foo"</literal></entry>
</row>
<row>
<entry><function>quote_literal</function>(<parameter>string</parameter> text)</entry>
<entry><type>text</type></entry>
<entry>
Return the given string suitably quoted to be used as a literal
in an <acronym>SQL</acronym> query string.
Embedded quotes and backslashes are properly doubled.
</entry>
<entry><literal>quote_literal('O\'Reilly')</literal></entry>
<entry><literal>'O''Reilly'</literal></entry>
</row>
<row>
<entry><function>repeat</function>(<type>text</type>, <type>integer</type>)</entry>
<entry><type>text</type></entry>
<entry>Repeat text a number of times</entry>
<entry><literal>repeat('Pg', 4)</literal></entry>
<entry><literal>PgPgPgPg</literal></entry>
</row>
<row>
<entry><function>replace</function>(<parameter>string</parameter> <type>text</type>,
<parameter>from</parameter> <type>text</type>,
<parameter>to</parameter> <type>text</type>)</entry>
<entry><type>text</type></entry>
<entry>Replace all occurrences in <parameter>string</parameter> of substring
<parameter>from</parameter> with substring <parameter>to</parameter>
</entry>
<entry><literal>replace('abcdefabcdef', 'cd', 'XX')</literal></entry>
<entry><literal>abXXefabXXef</literal></entry>
</row>
<row>
<entry>
<function>rpad</function>(<parameter>string</parameter> <type>text</type>,
<parameter>length</parameter> <type>integer</type>
<optional>, <parameter>fill</parameter> <type>text</type></optional>)
</entry>
<entry><type>text</type></entry>
<entry>
Fill up the <parameter>string</parameter> to length
<parameter>length</parameter> by appending the characters
<parameter>fill</parameter> (a space by default). If the
<parameter>string</parameter> is already longer than
<parameter>length</parameter> then it is truncated.
</entry>
<entry><literal>rpad('hi', 5, 'xy')</literal></entry>
<entry><literal>hixyx</literal></entry>
</row>
<row>
<entry><function>rtrim</function>(<parameter>string</parameter>
text, <parameter>trim</parameter> text)</entry>
<entry><type>text</type></entry>
<entry>
Remove the longest string containing only characters from
<parameter>trim</parameter> from the end of the string.
</entry>
<entry><literal>rtrim('trimxxxx','x')</literal></entry>
<entry><literal>trim</literal></entry>
</row>
<row>
<entry><function>split_part</function>(<parameter>string</parameter> <type>text</type>,
<parameter>delimiter</parameter> <type>text</type>,
<parameter>column</parameter> <type>integer</type>)</entry>
<entry><type>text</type></entry>
<entry>Split <parameter>string</parameter> on <parameter>delimiter</parameter>
returning the resulting (one based) <parameter>column</parameter> number.
</entry>
<entry><literal>split_part('abc~@~def~@~ghi','~@~',2)</literal></entry>
<entry><literal>def</literal></entry>
</row>
<row>
<entry><function>strpos</function>(<parameter>string</parameter>, <parameter>substring</parameter>)</entry>
<entry><type>text</type></entry>
<entry>
Locate specified substring (same as
<literal>position(<parameter>substring</parameter> in
<parameter>string</parameter>)</literal>, but note the reversed
argument order)
</entry>
<entry><literal>strpos('high','ig')</literal></entry>
<entry><literal>2</literal></entry>
</row>
<row>
<entry><function>substr</function>(<parameter>string</parameter>, <parameter>from</parameter> <optional>, <parameter>count</parameter></optional>)</entry>
<entry><type>text</type></entry>
<entry>
Extract specified substring (same as
<literal>substring(<parameter>string</parameter> from <parameter>from</parameter> for <parameter>count</parameter>)</literal>)
</entry>
<entry><literal>substr('alphabet', 3, 2)</literal></entry>
<entry><literal>ph</literal></entry>
</row>
<row>
<entry><function>to_ascii</function>(<type>text</type>
<optional>, <parameter>encoding</parameter></optional>)</entry>
<entry><type>text</type></entry>
<entry>
Convert text to <acronym>ASCII</acronym> from other encoding
<footnote>
<para>
The <function>to_ascii</function> function supports conversion from
<literal>LATIN1</>, <literal>LATIN2</>, and <literal>WIN1250</> only.
</para>
</footnote>
</entry>
<entry><literal>to_ascii('Karel')</literal></entry>
<entry><literal>Karel</literal></entry>
</row>
<row>
<entry><function>to_hex</function>(<parameter>number</parameter> <type>integer</type>
or <type>bigint</type>)</entry>
<entry><type>text</type></entry>
<entry>Convert <parameter>number</parameter> to its equivalent hexadecimal
representation
</entry>
<entry><literal>to_hex(9223372036854775807::bigint)</literal></entry>
<entry><literal>7fffffffffffffff</literal></entry>
</row>
<row>
<entry>
<function>translate</function>(<parameter>string</parameter>
<type>text</type>,
<parameter>from</parameter> <type>text</type>,
<parameter>to</parameter> <type>text</type>)
</entry>
<entry><type>text</type></entry>
<entry>
Any character in <parameter>string</parameter> that matches a
character in the <parameter>from</parameter> set is replaced by
the corresponding character in the <parameter>to</parameter>
set.
</entry>
<entry><literal>translate('12345', '14', 'ax')</literal></entry>
<entry><literal>a23x5</literal></entry>
</row>
</tbody>
</tgroup>
</table>
<table id="conversion-names">
<title>Built-in Conversions</title>
<tgroup cols="3">
<thead>
<row>
<entry>Conversion Name
<footnote>
<para>
The conversion names follow a standard naming scheme: The
official name of the source encoding with all
non-alphanumeric characters replaced by underscores followed
by <literal>_to_</literal> followed by the equally processed
destination encoding name. Therefore the names might deviate
from the customary encoding names.
</para>
</footnote>
</entry>
<entry>Source Encoding</entry>
<entry>Destination Encoding</entry>
</row>
</thead>
<tbody>
<row>
<entry><literal>ascii_to_mic</literal></entry>
<entry><literal>SQL_ASCII</literal></entry>
<entry><literal>MULE_INTERNAL</literal></entry>
</row>
<row>
<entry><literal>ascii_to_utf_8</literal></entry>
<entry><literal>SQL_ASCII</literal></entry>
<entry><literal>UNICODE</literal></entry>
</row>
<row>
<entry><literal>big5_to_euc_tw</literal></entry>
<entry><literal>BIG5</literal></entry>
<entry><literal>EUC_TW</literal></entry>
</row>
<row>
<entry><literal>big5_to_mic</literal></entry>
<entry><literal>BIG5</literal></entry>
<entry><literal>MULE_INTERNAL</literal></entry>
</row>
<row>
<entry><literal>big5_to_utf_8</literal></entry>
<entry><literal>BIG5</literal></entry>
<entry><literal>UNICODE</literal></entry>
</row>
<row>
<entry><literal>euc_cn_to_mic</literal></entry>
<entry><literal>EUC_CN</literal></entry>
<entry><literal>MULE_INTERNAL</literal></entry>
</row>
<row>
<entry><literal>euc_cn_to_utf_8</literal></entry>
<entry><literal>EUC_CN</literal></entry>
<entry><literal>UNICODE</literal></entry>
</row>
<row>
<entry><literal>euc_jp_to_mic</literal></entry>
<entry><literal>EUC_JP</literal></entry>
<entry><literal>MULE_INTERNAL</literal></entry>
</row>
<row>
<entry><literal>euc_jp_to_sjis</literal></entry>
<entry><literal>EUC_JP</literal></entry>
<entry><literal>SJIS</literal></entry>
</row>
<row>
<entry><literal>euc_jp_to_utf_8</literal></entry>
<entry><literal>EUC_JP</literal></entry>
<entry><literal>UNICODE</literal></entry>
</row>
<row>
<entry><literal>euc_kr_to_mic</literal></entry>
<entry><literal>EUC_KR</literal></entry>
<entry><literal>MULE_INTERNAL</literal></entry>
</row>
<row>
<entry><literal>euc_kr_to_utf_8</literal></entry>
<entry><literal>EUC_KR</literal></entry>
<entry><literal>UNICODE</literal></entry>
</row>
<row>
<entry><literal>euc_tw_to_big5</literal></entry>
<entry><literal>EUC_TW</literal></entry>
<entry><literal>BIG5</literal></entry>
</row>
<row>
<entry><literal>euc_tw_to_mic</literal></entry>
<entry><literal>EUC_TW</literal></entry>
<entry><literal>MULE_INTERNAL</literal></entry>
</row>
<row>
<entry><literal>euc_tw_to_utf_8</literal></entry>
<entry><literal>EUC_TW</literal></entry>
<entry><literal>UNICODE</literal></entry>
</row>
<row>
<entry><literal>gb18030_to_utf_8</literal></entry>
<entry><literal>GB18030</literal></entry>
<entry><literal>UNICODE</literal></entry>
</row>
<row>
<entry><literal>gbk_to_utf_8</literal></entry>
<entry><literal>GBK</literal></entry>
<entry><literal>UNICODE</literal></entry>
</row>
<row>
<entry><literal>iso_8859_10_to_utf_8</literal></entry>
<entry><literal>LATIN6</literal></entry>
<entry><literal>UNICODE</literal></entry>
</row>
<row>
<entry><literal>iso_8859_13_to_utf_8</literal></entry>
<entry><literal>LATIN7</literal></entry>
<entry><literal>UNICODE</literal></entry>
</row>
<row>
<entry><literal>iso_8859_14_to_utf_8</literal></entry>
<entry><literal>LATIN8</literal></entry>
<entry><literal>UNICODE</literal></entry>
</row>
<row>
<entry><literal>iso_8859_15_to_utf_8</literal></entry>
<entry><literal>LATIN9</literal></entry>
<entry><literal>UNICODE</literal></entry>
</row>
<row>
<entry><literal>iso_8859_16_to_utf_8</literal></entry>
<entry><literal>LATIN10</literal></entry>
<entry><literal>UNICODE</literal></entry>
</row>
<row>
<entry><literal>iso_8859_1_to_mic</literal></entry>
<entry><literal>LATIN1</literal></entry>
<entry><literal>MULE_INTERNAL</literal></entry>
</row>
<row>
<entry><literal>iso_8859_1_to_utf_8</literal></entry>
<entry><literal>LATIN1</literal></entry>
<entry><literal>UNICODE</literal></entry>
</row>
<row>
<entry><literal>iso_8859_2_to_mic</literal></entry>
<entry><literal>LATIN2</literal></entry>
<entry><literal>MULE_INTERNAL</literal></entry>
</row>
<row>
<entry><literal>iso_8859_2_to_utf_8</literal></entry>
<entry><literal>LATIN2</literal></entry>
<entry><literal>UNICODE</literal></entry>
</row>
<row>
<entry><literal>iso_8859_2_to_windows_1250</literal></entry>
<entry><literal>LATIN2</literal></entry>
<entry><literal>WIN1250</literal></entry>
</row>
<row>
<entry><literal>iso_8859_3_to_mic</literal></entry>
<entry><literal>LATIN3</literal></entry>
<entry><literal>MULE_INTERNAL</literal></entry>
</row>
<row>
<entry><literal>iso_8859_3_to_utf_8</literal></entry>
<entry><literal>LATIN3</literal></entry>
<entry><literal>UNICODE</literal></entry>
</row>
<row>
<entry><literal>iso_8859_4_to_mic</literal></entry>
<entry><literal>LATIN4</literal></entry>
<entry><literal>MULE_INTERNAL</literal></entry>
</row>
<row>
<entry><literal>iso_8859_4_to_utf_8</literal></entry>
<entry><literal>LATIN4</literal></entry>
<entry><literal>UNICODE</literal></entry>
</row>
<row>
<entry><literal>iso_8859_5_to_koi8_r</literal></entry>
<entry><literal>ISO_8859_5</literal></entry>
<entry><literal>KOI8</literal></entry>
</row>
<row>
<entry><literal>iso_8859_5_to_mic</literal></entry>
<entry><literal>ISO_8859_5</literal></entry>
<entry><literal>MULE_INTERNAL</literal></entry>
</row>
<row>
<entry><literal>iso_8859_5_to_utf_8</literal></entry>
<entry><literal>ISO_8859_5</literal></entry>
<entry><literal>UNICODE</literal></entry>
</row>
<row>
<entry><literal>iso_8859_5_to_windows_1251</literal></entry>
<entry><literal>ISO_8859_5</literal></entry>
<entry><literal>WIN</literal></entry>
</row>
<row>
<entry><literal>iso_8859_5_to_windows_866</literal></entry>
<entry><literal>ISO_8859_5</literal></entry>
<entry><literal>ALT</literal></entry>
</row>
<row>
<entry><literal>iso_8859_6_to_utf_8</literal></entry>
<entry><literal>ISO_8859_6</literal></entry>
<entry><literal>UNICODE</literal></entry>
</row>
<row>
<entry><literal>iso_8859_7_to_utf_8</literal></entry>
<entry><literal>ISO_8859_7</literal></entry>
<entry><literal>UNICODE</literal></entry>
</row>
<row>
<entry><literal>iso_8859_8_to_utf_8</literal></entry>
<entry><literal>ISO_8859_8</literal></entry>
<entry><literal>UNICODE</literal></entry>
</row>
<row>
<entry><literal>iso_8859_9_to_utf_8</literal></entry>
<entry><literal>LATIN5</literal></entry>
<entry><literal>UNICODE</literal></entry>
</row>
<row>
<entry><literal>johab_to_utf_8</literal></entry>
<entry><literal>JOHAB</literal></entry>
<entry><literal>UNICODE</literal></entry>
</row>
<row>
<entry><literal>koi8_r_to_iso_8859_5</literal></entry>
<entry><literal>KOI8</literal></entry>
<entry><literal>ISO_8859_5</literal></entry>
</row>
<row>
<entry><literal>koi8_r_to_mic</literal></entry>
<entry><literal>KOI8</literal></entry>
<entry><literal>MULE_INTERNAL</literal></entry>
</row>
<row>
<entry><literal>koi8_r_to_utf_8</literal></entry>
<entry><literal>KOI8</literal></entry>
<entry><literal>UNICODE</literal></entry>
</row>
<row>
<entry><literal>koi8_r_to_windows_1251</literal></entry>
<entry><literal>KOI8</literal></entry>
<entry><literal>WIN</literal></entry>
</row>
<row>
<entry><literal>koi8_r_to_windows_866</literal></entry>
<entry><literal>KOI8</literal></entry>
<entry><literal>ALT</literal></entry>
</row>
<row>
<entry><literal>mic_to_ascii</literal></entry>
<entry><literal>MULE_INTERNAL</literal></entry>
<entry><literal>SQL_ASCII</literal></entry>
</row>
<row>
<entry><literal>mic_to_big5</literal></entry>
<entry><literal>MULE_INTERNAL</literal></entry>
<entry><literal>BIG5</literal></entry>
</row>
<row>
<entry><literal>mic_to_euc_cn</literal></entry>
<entry><literal>MULE_INTERNAL</literal></entry>
<entry><literal>EUC_CN</literal></entry>
</row>
<row>
<entry><literal>mic_to_euc_jp</literal></entry>
<entry><literal>MULE_INTERNAL</literal></entry>
<entry><literal>EUC_JP</literal></entry>
</row>
<row>
<entry><literal>mic_to_euc_kr</literal></entry>
<entry><literal>MULE_INTERNAL</literal></entry>
<entry><literal>EUC_KR</literal></entry>
</row>
<row>
<entry><literal>mic_to_euc_tw</literal></entry>
<entry><literal>MULE_INTERNAL</literal></entry>
<entry><literal>EUC_TW</literal></entry>
</row>
<row>
<entry><literal>mic_to_iso_8859_1</literal></entry>
<entry><literal>MULE_INTERNAL</literal></entry>
<entry><literal>LATIN1</literal></entry>
</row>
<row>
<entry><literal>mic_to_iso_8859_2</literal></entry>
<entry><literal>MULE_INTERNAL</literal></entry>
<entry><literal>LATIN2</literal></entry>
</row>
<row>
<entry><literal>mic_to_iso_8859_3</literal></entry>
<entry><literal>MULE_INTERNAL</literal></entry>
<entry><literal>LATIN3</literal></entry>
</row>
<row>
<entry><literal>mic_to_iso_8859_4</literal></entry>
<entry><literal>MULE_INTERNAL</literal></entry>
<entry><literal>LATIN4</literal></entry>
</row>
<row>
<entry><literal>mic_to_iso_8859_5</literal></entry>
<entry><literal>MULE_INTERNAL</literal></entry>
<entry><literal>ISO_8859_5</literal></entry>
</row>
<row>
<entry><literal>mic_to_koi8_r</literal></entry>
<entry><literal>MULE_INTERNAL</literal></entry>
<entry><literal>KOI8</literal></entry>
</row>
<row>
<entry><literal>mic_to_sjis</literal></entry>
<entry><literal>MULE_INTERNAL</literal></entry>
<entry><literal>SJIS</literal></entry>
</row>
<row>
<entry><literal>mic_to_windows_1250</literal></entry>
<entry><literal>MULE_INTERNAL</literal></entry>
<entry><literal>WIN1250</literal></entry>
</row>
<row>
<entry><literal>mic_to_windows_1251</literal></entry>
<entry><literal>MULE_INTERNAL</literal></entry>
<entry><literal>WIN</literal></entry>
</row>
<row>
<entry><literal>mic_to_windows_866</literal></entry>
<entry><literal>MULE_INTERNAL</literal></entry>
<entry><literal>ALT</literal></entry>
</row>
<row>
<entry><literal>sjis_to_euc_jp</literal></entry>
<entry><literal>SJIS</literal></entry>
<entry><literal>EUC_JP</literal></entry>
</row>
<row>
<entry><literal>sjis_to_mic</literal></entry>
<entry><literal>SJIS</literal></entry>
<entry><literal>MULE_INTERNAL</literal></entry>
</row>
<row>
<entry><literal>sjis_to_utf_8</literal></entry>
<entry><literal>SJIS</literal></entry>
<entry><literal>UNICODE</literal></entry>
</row>
<row>
<entry><literal>tcvn_to_utf_8</literal></entry>
<entry><literal>TCVN</literal></entry>
<entry><literal>UNICODE</literal></entry>
</row>
<row>
<entry><literal>uhc_to_utf_8</literal></entry>
<entry><literal>UHC</literal></entry>
<entry><literal>UNICODE</literal></entry>
</row>
<row>
<entry><literal>utf_8_to_ascii</literal></entry>
<entry><literal>UNICODE</literal></entry>
<entry><literal>SQL_ASCII</literal></entry>
</row>
<row>
<entry><literal>utf_8_to_big5</literal></entry>
<entry><literal>UNICODE</literal></entry>
<entry><literal>BIG5</literal></entry>
</row>
<row>
<entry><literal>utf_8_to_euc_cn</literal></entry>
<entry><literal>UNICODE</literal></entry>
<entry><literal>EUC_CN</literal></entry>
</row>
<row>
<entry><literal>utf_8_to_euc_jp</literal></entry>
<entry><literal>UNICODE</literal></entry>
<entry><literal>EUC_JP</literal></entry>
</row>
<row>
<entry><literal>utf_8_to_euc_kr</literal></entry>
<entry><literal>UNICODE</literal></entry>
<entry><literal>EUC_KR</literal></entry>
</row>
<row>
<entry><literal>utf_8_to_euc_tw</literal></entry>
<entry><literal>UNICODE</literal></entry>
<entry><literal>EUC_TW</literal></entry>
</row>
<row>
<entry><literal>utf_8_to_gb18030</literal></entry>
<entry><literal>UNICODE</literal></entry>
<entry><literal>GB18030</literal></entry>
</row>
<row>
<entry><literal>utf_8_to_gbk</literal></entry>
<entry><literal>UNICODE</literal></entry>
<entry><literal>GBK</literal></entry>
</row>
<row>
<entry><literal>utf_8_to_iso_8859_1</literal></entry>
<entry><literal>UNICODE</literal></entry>
<entry><literal>LATIN1</literal></entry>
</row>
<row>
<entry><literal>utf_8_to_iso_8859_10</literal></entry>
<entry><literal>UNICODE</literal></entry>
<entry><literal>LATIN6</literal></entry>
</row>
<row>
<entry><literal>utf_8_to_iso_8859_13</literal></entry>
<entry><literal>UNICODE</literal></entry>
<entry><literal>LATIN7</literal></entry>
</row>
<row>
<entry><literal>utf_8_to_iso_8859_14</literal></entry>
<entry><literal>UNICODE</literal></entry>
<entry><literal>LATIN8</literal></entry>
</row>
<row>
<entry><literal>utf_8_to_iso_8859_15</literal></entry>
<entry><literal>UNICODE</literal></entry>
<entry><literal>LATIN9</literal></entry>
</row>
<row>
<entry><literal>utf_8_to_iso_8859_16</literal></entry>
<entry><literal>UNICODE</literal></entry>
<entry><literal>LATIN10</literal></entry>
</row>
<row>
<entry><literal>utf_8_to_iso_8859_2</literal></entry>
<entry><literal>UNICODE</literal></entry>
<entry><literal>LATIN2</literal></entry>
</row>
<row>
<entry><literal>utf_8_to_iso_8859_3</literal></entry>
<entry><literal>UNICODE</literal></entry>
<entry><literal>LATIN3</literal></entry>
</row>
<row>
<entry><literal>utf_8_to_iso_8859_4</literal></entry>
<entry><literal>UNICODE</literal></entry>
<entry><literal>LATIN4</literal></entry>
</row>
<row>
<entry><literal>utf_8_to_iso_8859_5</literal></entry>
<entry><literal>UNICODE</literal></entry>
<entry><literal>ISO_8859_5</literal></entry>
</row>
<row>
<entry><literal>utf_8_to_iso_8859_6</literal></entry>
<entry><literal>UNICODE</literal></entry>
<entry><literal>ISO_8859_6</literal></entry>
</row>
<row>
<entry><literal>utf_8_to_iso_8859_7</literal></entry>
<entry><literal>UNICODE</literal></entry>
<entry><literal>ISO_8859_7</literal></entry>
</row>
<row>
<entry><literal>utf_8_to_iso_8859_8</literal></entry>
<entry><literal>UNICODE</literal></entry>
<entry><literal>ISO_8859_8</literal></entry>
</row>
<row>
<entry><literal>utf_8_to_iso_8859_9</literal></entry>
<entry><literal>UNICODE</literal></entry>
<entry><literal>LATIN5</literal></entry>
</row>
<row>
<entry><literal>utf_8_to_johab</literal></entry>
<entry><literal>UNICODE</literal></entry>
<entry><literal>JOHAB</literal></entry>
</row>
<row>
<entry><literal>utf_8_to_koi8_r</literal></entry>
<entry><literal>UNICODE</literal></entry>
<entry><literal>KOI8</literal></entry>
</row>
<row>
<entry><literal>utf_8_to_sjis</literal></entry>
<entry><literal>UNICODE</literal></entry>
<entry><literal>SJIS</literal></entry>
</row>
<row>
<entry><literal>utf_8_to_tcvn</literal></entry>
<entry><literal>UNICODE</literal></entry>
<entry><literal>TCVN</literal></entry>
</row>
<row>
<entry><literal>utf_8_to_uhc</literal></entry>
<entry><literal>UNICODE</literal></entry>
<entry><literal>UHC</literal></entry>
</row>
<row>
<entry><literal>utf_8_to_windows_1250</literal></entry>
<entry><literal>UNICODE</literal></entry>
<entry><literal>WIN1250</literal></entry>
</row>
<row>
<entry><literal>utf_8_to_windows_1251</literal></entry>
<entry><literal>UNICODE</literal></entry>
<entry><literal>WIN</literal></entry>
</row>
<row>
<entry><literal>utf_8_to_windows_1256</literal></entry>
<entry><literal>UNICODE</literal></entry>
<entry><literal>WIN1256</literal></entry>
</row>
<row>
<entry><literal>utf_8_to_windows_866</literal></entry>
<entry><literal>UNICODE</literal></entry>
<entry><literal>ALT</literal></entry>
</row>
<row>
<entry><literal>utf_8_to_windows_874</literal></entry>
<entry><literal>UNICODE</literal></entry>
<entry><literal>WIN874</literal></entry>
</row>
<row>
<entry><literal>windows_1250_to_iso_8859_2</literal></entry>
<entry><literal>WIN1250</literal></entry>
<entry><literal>LATIN2</literal></entry>
</row>
<row>
<entry><literal>windows_1250_to_mic</literal></entry>
<entry><literal>WIN1250</literal></entry>
<entry><literal>MULE_INTERNAL</literal></entry>
</row>
<row>
<entry><literal>windows_1250_to_utf_8</literal></entry>
<entry><literal>WIN1250</literal></entry>
<entry><literal>UNICODE</literal></entry>
</row>
<row>
<entry><literal>windows_1251_to_iso_8859_5</literal></entry>
<entry><literal>WIN</literal></entry>
<entry><literal>ISO_8859_5</literal></entry>
</row>
<row>
<entry><literal>windows_1251_to_koi8_r</literal></entry>
<entry><literal>WIN</literal></entry>
<entry><literal>KOI8</literal></entry>
</row>
<row>
<entry><literal>windows_1251_to_mic</literal></entry>
<entry><literal>WIN</literal></entry>
<entry><literal>MULE_INTERNAL</literal></entry>
</row>
<row>
<entry><literal>windows_1251_to_utf_8</literal></entry>
<entry><literal>WIN</literal></entry>
<entry><literal>UNICODE</literal></entry>
</row>
<row>
<entry><literal>windows_1251_to_windows_866</literal></entry>
<entry><literal>WIN</literal></entry>
<entry><literal>ALT</literal></entry>
</row>
<row>
<entry><literal>windows_1256_to_utf_8</literal></entry>
<entry><literal>WIN1256</literal></entry>
<entry><literal>UNICODE</literal></entry>
</row>
<row>
<entry><literal>windows_866_to_iso_8859_5</literal></entry>
<entry><literal>ALT</literal></entry>
<entry><literal>ISO_8859_5</literal></entry>
</row>
<row>
<entry><literal>windows_866_to_koi8_r</literal></entry>
<entry><literal>ALT</literal></entry>
<entry><literal>KOI8</literal></entry>
</row>
<row>
<entry><literal>windows_866_to_mic</literal></entry>
<entry><literal>ALT</literal></entry>
<entry><literal>MULE_INTERNAL</literal></entry>
</row>
<row>
<entry><literal>windows_866_to_utf_8</literal></entry>
<entry><literal>ALT</literal></entry>
<entry><literal>UNICODE</literal></entry>
</row>
<row>
<entry><literal>windows_866_to_windows_1251</literal></entry>
<entry><literal>ALT</literal></entry>
<entry><literal>WIN</literal></entry>
</row>
<row>
<entry><literal>windows_874_to_utf_8</literal></entry>
<entry><literal>WIN874</literal></entry>
<entry><literal>UNICODE</literal></entry>
</row>
</tbody>
</tgroup>
</table>
</sect1>
<sect1 id="functions-binarystring">
<title>Binary String Functions and Operators</title>
<para>
This section describes functions and operators for examining and
manipulating binary string values. Strings in this context mean
values of the type <type>BYTEA</type>.
</para>
<para>
<acronym>SQL</acronym> defines some string functions with a
special syntax where
certain key words rather than commas are used to separate the
arguments. Details are in
<xref linkend="functions-binarystring-sql">.
Some functions are also implemented using the regular syntax for
function invocation.
(See <xref linkend="functions-binarystring-other">.)
</para>
<table id="functions-binarystring-sql">
<title><acronym>SQL</acronym> Binary String Functions and Operators</title>
<tgroup cols="5">
<thead>
<row>
<entry>Function</entry>
<entry>Return Type</entry>
<entry>Description</entry>
<entry>Example</entry>
<entry>Result</entry>
</row>
</thead>
<tbody>
<row>
<entry> <parameter>string</parameter> <literal>||</literal>
<parameter>string</parameter> </entry>
<entry> <type>bytea</type> </entry>
<entry>
String concatenation
<indexterm>
<primary>binary strings</primary>
<secondary>concatenation</secondary>
</indexterm>
</entry>
<entry><literal>'\\\\Post'::bytea || '\\047greSQL\\000'::bytea</literal></entry>
<entry><literal>\\Post'greSQL\000</literal></entry>
</row>
<row>
<entry><function>octet_length</function>(<parameter>string</parameter>)</entry>
<entry><type>integer</type></entry>
<entry>Number of bytes in binary string</entry>
<entry><literal>octet_length('jo\\000se'::bytea)</literal></entry>
<entry><literal>5</literal></entry>
</row>
<row>
<entry><function>position</function>(<parameter>substring</parameter> in <parameter>string</parameter>)</entry>
<entry><type>integer</type></entry>
<entry>Location of specified substring</entry>
<entry><literal>position('\\000om'::bytea in 'Th\\000omas'::bytea)</literal></entry>
<entry><literal>3</literal></entry>
</row>
<row>
<entry><function>substring</function>(<parameter>string</parameter> <optional>from <type>integer</type></optional> <optional>for <type>integer</type></optional>)</entry>
<entry><type>bytea</type></entry>
<entry>
Extract substring
<indexterm>
<primary>substring</primary>
</indexterm>
</entry>
<entry><literal>substring('Th\\000omas'::bytea from 2 for 3)</literal></entry>
<entry><literal>h\000o</literal></entry>
</row>
<row>
<entry>
<function>trim</function>(<optional>both</optional>
<parameter>characters</parameter> from
<parameter>string</parameter>)
</entry>
<entry><type>bytea</type></entry>
<entry>
Remove the longest string containing only the
<parameter>characters</parameter> from the
beginning/end/both ends of the <parameter>string</parameter>
</entry>
<entry><literal>trim('\\000'::bytea from '\\000Tom\\000'::bytea)</literal></entry>
<entry><literal>Tom</literal></entry>
</row>
<row>
<entry><function>get_byte</function>(<parameter>string</parameter>, <parameter>offset</parameter>)</entry>
<entry><type>integer</type></entry>
<entry>
Extract byte from string.
<indexterm>
<primary>get_byte</primary>
</indexterm>
</entry>
<entry><literal>get_byte('Th\\000omas'::bytea, 4)</literal></entry>
<entry><literal>109</literal></entry>
</row>
<row>
<entry><function>set_byte</function>(<parameter>string</parameter>,
<parameter>offset</parameter>, <parameter>newvalue</>)</entry>
<entry><type>bytea</type></entry>
<entry>
Set byte in string.
<indexterm>
<primary>set_byte</primary>
</indexterm>
</entry>
<entry><literal>set_byte('Th\\000omas'::bytea, 4, 64)</literal></entry>
<entry><literal>Th\000o@as</literal></entry>
</row>
<row>
<entry><function>get_bit</function>(<parameter>string</parameter>, <parameter>offset</parameter>)</entry>
<entry><type>integer</type></entry>
<entry>
Extract bit from string.
<indexterm>
<primary>get_bit</primary>
</indexterm>
</entry>
<entry><literal>get_bit('Th\\000omas'::bytea, 45)</literal></entry>
<entry><literal>1</literal></entry>
</row>
<row>
<entry><function>set_bit</function>(<parameter>string</parameter>,
<parameter>offset</parameter>, <parameter>newvalue</>)</entry>
<entry><type>bytea</type></entry>
<entry>
Set bit in string.
<indexterm>
<primary>set_bit</primary>
</indexterm>
</entry>
<entry><literal>set_bit('Th\\000omas'::bytea, 45, 0)</literal></entry>
<entry><literal>Th\000omAs</literal></entry>
</row>
</tbody>
</tgroup>
</table>
<para>
Additional binary string manipulation functions are available and
are listed in <xref linkend="functions-binarystring-other">. Some
of them are used internally to implement the
<acronym>SQL</acronym>-standard string functions listed in <xref
linkend="functions-binarystring-sql">.
</para>
<table id="functions-binarystring-other">
<title>Other Binary String Functions</title>
<tgroup cols="5">
<thead>
<row>
<entry>Function</entry>
<entry>Return Type</entry>
<entry>Description</entry>
<entry>Example</entry>
<entry>Result</entry>
</row>
</thead>
<tbody>
<row>
<entry><function>btrim</function>(<parameter>string</parameter>
<type>bytea</type> <parameter>trim</parameter> <type>bytea</type>)</entry>
<entry><type>bytea</type></entry>
<entry>
Remove (trim) the longest string consisting only of characters
in <parameter>trim</parameter> from the start and end of
<parameter>string</parameter>.
</entry>
<entry><literal>btrim('\\000trim\\000'::bytea,'\\000'::bytea)</literal></entry>
<entry><literal>trim</literal></entry>
</row>
<row>
<entry><function>length</function>(<parameter>string</parameter>)</entry>
<entry><type>integer</type></entry>
<entry>
Length of binary string
<indexterm>
<primary>binary strings</primary>
<secondary>length</secondary>
</indexterm>
<indexterm>
<primary>length</primary>
<secondary>binary strings</secondary>
<see>binary strings, length</see>
</indexterm>
</entry>
<entry><literal>length('jo\\000se'::bytea)</literal></entry>
<entry><literal>5</literal></entry>
</row>
<row>
<entry>
<function>encode</function>(<parameter>string</parameter> <type>bytea</type>,
<parameter>type</parameter> <type>text</type>)
</entry>
<entry><type>text</type></entry>
<entry>
Encode binary string to <acronym>ASCII</acronym>-only representation. Supported
types are: base64, hex, escape.
</entry>
<entry><literal>encode('123\\000456'::bytea, 'escape')</literal></entry>
<entry><literal>123\000456</literal></entry>
</row>
<row>
<entry>
<function>decode</function>(<parameter>string</parameter> <type>text</type>,
<parameter>type</parameter> <type>text</type>)
</entry>
<entry><type>bytea</type></entry>
<entry>
Decode binary string from <parameter>string</parameter> previously
encoded with <literal>encode()</>. Parameter type is same as in <literal>encode()</>.
</entry>
<entry><literal>decode('123\\000456', 'escape')</literal></entry>
<entry><literal>123\000456</literal></entry>
</row>
</tbody>
</tgroup>
</table>
</sect1>
<sect1 id="functions-matching">
<title>Pattern Matching</title>
<para>
There are three separate approaches to pattern matching provided by
<productname>PostgreSQL</productname>: the traditional
<acronym>SQL</acronym>
<function>LIKE</function> operator, the more recent
<acronym>SQL99</acronym>
<function>SIMILAR TO</function> operator, and
<acronym>POSIX</acronym>-style regular expressions.
Additionally, a pattern matching function,
<function>SUBSTRING</function>, is available, using either
<acronym>SQL99</acronym>-style or POSIX-style regular expressions.
</para>
<tip>
<para>
If you have pattern matching needs that go beyond this,
consider writing a user-defined function in Perl or Tcl.
</para>
</tip>
<sect2 id="functions-like">
<title><function>LIKE</function></title>
<indexterm>
<primary>like</primary>
</indexterm>
<synopsis>
<replaceable>string</replaceable> LIKE <replaceable>pattern</replaceable> <optional>ESCAPE <replaceable>escape-character</replaceable></optional>
<replaceable>string</replaceable> NOT LIKE <replaceable>pattern</replaceable> <optional>ESCAPE <replaceable>escape-character</replaceable></optional>
</synopsis>
<para>
Every <replaceable>pattern</replaceable> defines a set of strings.
The <function>LIKE</function> expression returns true if the
<replaceable>string</replaceable> is contained in the set of
strings represented by <replaceable>pattern</replaceable>. (As
expected, the <function>NOT LIKE</function> expression returns
false if <function>LIKE</function> returns true, and vice versa.
An equivalent expression is
<literal>NOT (<replaceable>string</replaceable> LIKE
<replaceable>pattern</replaceable>)</literal>.)
</para>
<para>
If <replaceable>pattern</replaceable> does not contain percent
signs or underscore, then the pattern only represents the string
itself; in that case <function>LIKE</function> acts like the
equals operator. An underscore (<literal>_</literal>) in
<replaceable>pattern</replaceable> stands for (matches) any single
character; a percent sign (<literal>%</literal>) matches any string
of zero or more characters.
</para>
<para>
Some examples:
<programlisting>
'abc' LIKE 'abc' <lineannotation>true</lineannotation>
'abc' LIKE 'a%' <lineannotation>true</lineannotation>
'abc' LIKE '_b_' <lineannotation>true</lineannotation>
'abc' LIKE 'c' <lineannotation>false</lineannotation>
</programlisting>
</para>
<para>
<function>LIKE</function> pattern matches always cover the entire
string. To match a pattern anywhere within a string, the
pattern must therefore start and end with a percent sign.
</para>
<para>
To match a literal underscore or percent sign without matching
other characters, the respective character in
<replaceable>pattern</replaceable> must be
preceded by the escape character. The default escape
character is the backslash but a different one may be selected by
using the <literal>ESCAPE</literal> clause. To match the escape
character itself, write two escape characters.
</para>
<para>
Note that the backslash already has a special meaning in string
literals, so to write a pattern constant that contains a backslash
you must write two backslashes in the query. Thus, writing a pattern
that actually matches a literal backslash means writing four backslashes
in the query. You can avoid this by selecting a different escape
character with <literal>ESCAPE</literal>; then backslash is not special
to <function>LIKE</function> anymore. (But it is still special to the string
literal parser, so you still need two of them.)
</para>
<para>
It's also possible to select no escape character by writing
<literal>ESCAPE ''</literal>. This effectively disables the
escape mechanism, which makes it impossible to turn off the
special meaning of underscore and percent signs in the pattern.
</para>
<para>
The keyword <token>ILIKE</token> can be used instead of
<token>LIKE</token> to make the match case insensitive according
to the active locale. This is not in the <acronym>SQL</acronym> standard but is a
<productname>PostgreSQL</productname> extension.
</para>
<para>
The operator <literal>~~</literal> is equivalent to
<function>LIKE</function>, and <literal>~~*</literal> corresponds to
<function>ILIKE</function>. There are also
<literal>!~~</literal> and <literal>!~~*</literal> operators that
represent <function>NOT LIKE</function> and <function>NOT
ILIKE</function>. All of these operators are
<productname>PostgreSQL</productname>-specific.
</para>
</sect2>
<sect2 id="functions-sql99-regexp">
<title><function>SIMILAR TO</function> and <acronym>SQL99</acronym>
Regular Expressions</title>
<indexterm zone="functions-sql99-regexp">
<primary>regular expressions</primary>
<!-- <seealso>pattern matching</seealso> breaks index build -->
</indexterm>
<indexterm>
<primary>similar to</primary>
</indexterm>
<indexterm>
<primary>substring</primary>
</indexterm>
<synopsis>
<replaceable>string</replaceable> SIMILAR TO <replaceable>pattern</replaceable> <optional>ESCAPE <replaceable>escape-character</replaceable></optional>
<replaceable>string</replaceable> NOT SIMILAR TO <replaceable>pattern</replaceable> <optional>ESCAPE <replaceable>escape-character</replaceable></optional>
</synopsis>
<para>
The <function>SIMILAR TO</function> operator returns true or false
depending on whether its pattern matches the given string. It is
much like <function>LIKE</function>, except that it interprets the
pattern using <acronym>SQL99</acronym>'s definition of a regular
expression.
<acronym>SQL99</acronym>'s regular expressions are a curious cross
between <function>LIKE</function> notation and common regular expression
notation.
</para>
<para>
Like <function>LIKE</function>, the <function>SIMILAR TO</function>
operator succeeds only if its pattern matches the entire string;
this is unlike common regular expression practice, wherein the pattern
may match any part of the string.
Also like
<function>LIKE</function>, <function>SIMILAR TO</function> uses
<literal>%</> and <literal>_</> as wildcard characters denoting
any string and any single character, respectively (these are
comparable to <literal>.*</> and <literal>.</> in POSIX regular
expressions).
</para>
<para>
In addition to these facilities borrowed from <function>LIKE</function>,
<function>SIMILAR TO</function> supports these pattern-matching
metacharacters borrowed from POSIX regular expressions:
<itemizedlist>
<listitem>
<para>
<literal>|</literal> denotes alternation (either of two alternatives).
</para>
</listitem>
<listitem>
<para>
<literal>*</literal> denotes repetition of the previous item zero
or more times.
</para>
</listitem>
<listitem>
<para>
<literal>+</literal> denotes repetition of the previous item one
or more times.
</para>
</listitem>
<listitem>
<para>
Parentheses <literal>()</literal> may be used to group items into
a single logical item.
</para>
</listitem>
<listitem>
<para>
A bracket expression <literal>[...]</literal> specifies a character
class, just as in POSIX regular expressions.
</para>
</listitem>
</itemizedlist>
Notice that bounded repetition (<literal>?</> and <literal>{...}</>)
are not provided, though they exist in POSIX. Also, dot (<literal>.</>)
is not a metacharacter.
</para>
<para>
As with <function>LIKE</>, a backslash disables the special meaning
of any of these metacharacters; or a different escape character can
be specified with <literal>ESCAPE</>.
</para>
<para>
Some examples:
<programlisting>
'abc' SIMILAR TO 'abc' <lineannotation>true</lineannotation>
'abc' SIMILAR TO 'a' <lineannotation>false</lineannotation>
'abc' SIMILAR TO '%(b|d)%' <lineannotation>true</lineannotation>
'abc' SIMILAR TO '(b|c)%' <lineannotation>false</lineannotation>
</programlisting>
</para>
<para>
The <function>SUBSTRING</> function with three parameters,
<function>SUBSTRING(<parameter>string</parameter> FROM
<replaceable>pattern</replaceable> FOR
<replaceable>escape</replaceable>)</function>, provides
extraction of a substring that matches a <acronym>SQL99</acronym>
regular expression pattern. As with <literal>SIMILAR TO</>, the
specified pattern must match to the entire data string, else the
function fails and returns null. To indicate the part of the
pattern that should be returned on success,
<acronym>SQL99</acronym> specifies that the pattern must contain
two occurrences of the escape character followed by double quote
(<literal>"</>). The text matching the portion of the pattern
between these markers is returned.
</para>
<para>
Some examples:
<programlisting>
SUBSTRING('foobar' FROM '%#"o_b#"%' FOR '#') <lineannotation>oob</lineannotation>
SUBSTRING('foobar' FROM '#"o_b#"%' FOR '#') <lineannotation>NULL</lineannotation>
</programlisting>
</para>
</sect2>
<sect2 id="functions-posix-regexp">
<title><acronym>POSIX</acronym> Regular Expressions</title>
<indexterm zone="functions-posix-regexp">
<primary>regular expressions</primary>
<seealso>pattern matching</seealso>
</indexterm>
<para>
<xref linkend="functions-posix-table"> lists the available
operators for pattern matching using POSIX regular expressions.
</para>
<table id="functions-posix-table">
<title>Regular Expression Match Operators</title>
<tgroup cols="3">
<thead>
<row>
<entry>Operator</entry>
<entry>Description</entry>
<entry>Example</entry>
</row>
</thead>
<tbody>
<row>
<entry> <literal>~</literal> </entry>
<entry>Matches regular expression, case sensitive</entry>
<entry><literal>'thomas' ~ '.*thomas.*'</literal></entry>
</row>
<row>
<entry> <literal>~*</literal> </entry>
<entry>Matches regular expression, case insensitive</entry>
<entry><literal>'thomas' ~* '.*Thomas.*'</literal></entry>
</row>
<row>
<entry> <literal>!~</literal> </entry>
<entry>Does not match regular expression, case sensitive</entry>
<entry><literal>'thomas' !~ '.*Thomas.*'</literal></entry>
</row>
<row>
<entry> <literal>!~*</literal> </entry>
<entry>Does not match regular expression, case insensitive</entry>
<entry><literal>'thomas' !~* '.*vadim.*'</literal></entry>
</row>
</tbody>
</tgroup>
</table>
<para>
<acronym>POSIX</acronym> regular expressions provide a more
powerful means for
pattern matching than the <function>LIKE</function> and
<function>SIMILAR TO</> operators.
Many Unix tools such as <command>egrep</command>,
<command>sed</command>, or <command>awk</command> use a pattern
matching language that is similar to the one described here.
</para>
<para>
A regular expression is a character sequence that is an
abbreviated definition of a set of strings (a <firstterm>regular
set</firstterm>). A string is said to match a regular expression
if it is a member of the regular set described by the regular
expression. As with <function>LIKE</function>, pattern characters
match string characters exactly unless they are special characters
in the regular expression language --- but regular expressions use
different special characters than <function>LIKE</function> does.
Unlike <function>LIKE</function> patterns, a
regular expression is allowed to match anywhere within a string, unless
the regular expression is explicitly anchored to the beginning or
end of the string.
</para>
<para>
Some examples:
<programlisting>
'abc' ~ 'abc' <lineannotation>true</lineannotation>
'abc' ~ '^a' <lineannotation>true</lineannotation>
'abc' ~ '(b|d)' <lineannotation>true</lineannotation>
'abc' ~ '^(b|c)' <lineannotation>false</lineannotation>
</programlisting>
</para>
<para>
The <function>SUBSTRING</> function with two parameters,
<function>SUBSTRING(<parameter>string</parameter> FROM
<replaceable>pattern</replaceable>)</function>, provides extraction of a substring
that matches a POSIX regular expression pattern. It returns null if
there is no match, otherwise the portion of the text that matched the
pattern. But if the pattern contains any parentheses, the portion
of the text that matched the first parenthesized subexpression (the
one whose left parenthesis comes first) is
returned. You can always put parentheses around the whole expression
if you want to use parentheses within it without triggering this
exception. Also see the non-capturing parentheses described below.
</para>
<para>
Some examples:
<programlisting>
SUBSTRING('foobar' FROM 'o.b') <lineannotation>oob</lineannotation>
SUBSTRING('foobar' FROM 'o(.)b') <lineannotation>o</lineannotation>
</programlisting>
</para>
<para>
<productname>PostgreSQL</productname>'s regular expressions are implemented
using a package written by Henry Spencer. Much of
the description of regular expressions below is copied verbatim from his
manual entry.
</para>
<!-- derived from the re_syntax.n man page -->
<sect3 id="posix-syntax-details">
<title>Regular Expression Details</title>
<para>
Regular expressions (<acronym>RE</acronym>s), as defined in
<acronym>POSIX</acronym> 1003.2, come in two forms:
<firstterm>extended</> <acronym>RE</acronym>s or <acronym>ERE</>s
(roughly those of <command>egrep</command>), and
<firstterm>basic</> <acronym>RE</acronym>s or <acronym>BRE</>s
(roughly those of <command>ed</command>).
<productname>PostgreSQL</productname> supports both forms, and
also implements some extensions
that are not in the POSIX standard, but have become widely used anyway
due to their availability in programming languages such as Perl and Tcl.
<acronym>RE</acronym>s using these non-POSIX extensions are called
<firstterm>advanced</> <acronym>RE</acronym>s or <acronym>ARE</>s
in this documentation. AREs are almost an exact superset of EREs,
but BREs have several notational incompatibilities (as well as being
much more limited).
We first describe the ARE and ERE forms, noting features that apply
only to AREs, and then describe how BREs differ.
</para>
<note>
<para>
The form of regular expressions accepted by <productname>PostgreSQL</>
can be chosen by setting the <varname>REGEX_FLAVOR</> run-time parameter
(described in the &cite-admin;). The usual setting is
<literal>advanced</>, but one might choose <literal>extended</> for
maximum backwards compatibility with pre-7.4 releases of
<productname>PostgreSQL</>.
</para>
</note>
<para>
A regular expression is defined as one or more
<firstterm>branches</firstterm>, separated by
<literal>|</literal>. It matches anything that matches one of the
branches.
</para>
<para>
A branch is zero or more <firstterm>quantified atoms</> or
<firstterm>constraints</>, concatenated.
It matches a match for the first, followed by a match for the second, etc;
an empty branch matches the empty string.
</para>
<para>
A quantified atom is an <firstterm>atom</> possibly followed
by a single <firstterm>quantifier</>.
Without a quantifier, it matches a match for the atom.
With a quantifier, it can match some number of matches of the atom.
An <firstterm>atom</firstterm> can be any of the possibilities
shown in <xref linkend="posix-atoms-table">.
The possible quantifiers and their meanings are shown in
<xref linkend="posix-quantifiers-table">.
</para>
<para>
A <firstterm>constraint</> matches an empty string, but matches only when
specific conditions are met. A constraint can be used where an atom
could be used, except it may not be followed by a quantifier.
The simple constraints are shown in
<xref linkend="posix-constraints-table">;
some more constraints are described later.
</para>
<table id="posix-atoms-table">
<title>Regular Expression Atoms</title>
<tgroup cols="2">
<thead>
<row>
<entry>Atom</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry> <literal>(</><replaceable>re</><literal>)</> </entry>
<entry> (where <replaceable>re</> is any regular expression)
matches a match for
<replaceable>re</>, with the match noted for possible reporting </entry>
</row>
<row>
<entry> <literal>(?:</><replaceable>re</><literal>)</> </entry>
<entry> as above, but the match is not noted for reporting
(a <quote>non-capturing</> set of parentheses)
(AREs only) </entry>
</row>
<row>
<entry> <literal>.</> </entry>
<entry> matches any single character </entry>
</row>
<row>
<entry> <literal>[</><replaceable>chars</><literal>]</> </entry>
<entry> a <firstterm>bracket expression</>,
matching any one of the <replaceable>chars</> (see
<xref linkend="posix-bracket-expressions"> for more detail) </entry>
</row>
<row>
<entry> <literal>\</><replaceable>k</> </entry>
<entry> (where <replaceable>k</> is a non-alphanumeric character)
matches that character taken as an ordinary character,
e.g. <literal>\\</> matches a backslash character </entry>
</row>
<row>
<entry> <literal>\</><replaceable>c</> </entry>
<entry> where <replaceable>c</> is alphanumeric
(possibly followed by other characters)
is an <firstterm>escape</>, see <xref linkend="posix-escape-sequences">
(AREs only; in EREs and BREs, this matches <replaceable>c</>) </entry>
</row>
<row>
<entry> <literal>{</> </entry>
<entry> when followed by a character other than a digit,
matches the left-brace character <literal>{</>;
when followed by a digit, it is the beginning of a
<replaceable>bound</> (see below) </entry>
</row>
<row>
<entry> <replaceable>x</> </entry>
<entry> where <replaceable>x</> is a single character with no other
significance, matches that character </entry>
</row>
</tbody>
</tgroup>
</table>
<para>
An RE may not end with <literal>\</>.
</para>
<note>
<para>
Remember that the backslash (<literal>\</literal>) already has a special
meaning in <productname>PostgreSQL</> string literals.
To write a pattern constant that contains a backslash,
you must write two backslashes in the query.
</para>
</note>
<table id="posix-quantifiers-table">
<title>Regular Expression Quantifiers</title>
<tgroup cols="2">
<thead>
<row>
<entry>Quantifier</entry>
<entry>Matches</entry>
</row>
</thead>
<tbody>
<row>
<entry> <literal>*</> </entry>
<entry> a sequence of 0 or more matches of the atom </entry>
</row>
<row>
<entry> <literal>+</> </entry>
<entry> a sequence of 1 or more matches of the atom </entry>
</row>
<row>
<entry> <literal>?</> </entry>
<entry> a sequence of 0 or 1 matches of the atom </entry>
</row>
<row>
<entry> <literal>{</><replaceable>m</><literal>}</> </entry>
<entry> a sequence of exactly <replaceable>m</> matches of the atom </entry>
</row>
<row>
<entry> <literal>{</><replaceable>m</><literal>,}</> </entry>
<entry> a sequence of <replaceable>m</> or more matches of the atom </entry>
</row>
<row>
<entry>
<literal>{</><replaceable>m</><literal>,</><replaceable>n</><literal>}</> </entry>
<entry> a sequence of <replaceable>m</> through <replaceable>n</>
(inclusive) matches of the atom; <replaceable>m</> may not exceed
<replaceable>n</> </entry>
</row>
<row>
<entry> <literal>*?</> </entry>
<entry> non-greedy version of <literal>*</> </entry>
</row>
<row>
<entry> <literal>+?</> </entry>
<entry> non-greedy version of <literal>+</> </entry>
</row>
<row>
<entry> <literal>??</> </entry>
<entry> non-greedy version of <literal>?</> </entry>
</row>
<row>
<entry> <literal>{</><replaceable>m</><literal>}?</> </entry>
<entry> non-greedy version of <literal>{</><replaceable>m</><literal>}</> </entry>
</row>
<row>
<entry> <literal>{</><replaceable>m</><literal>,}?</> </entry>
<entry> non-greedy version of <literal>{</><replaceable>m</><literal>,}</> </entry>
</row>
<row>
<entry>
<literal>{</><replaceable>m</><literal>,</><replaceable>n</><literal>}?</> </entry>
<entry> non-greedy version of <literal>{</><replaceable>m</><literal>,</><replaceable>n</><literal>}</> </entry>
</row>
</tbody>
</tgroup>
</table>
<para>
The forms using <literal>{</><replaceable>...</><literal>}</>
are known as <firstterm>bound</>s.
The numbers <replaceable>m</> and <replaceable>n</> within a bound are
unsigned decimal integers with permissible values from 0 to 255 inclusive.
</para>
<para>
<firstterm>Non-greedy</> quantifiers (available in AREs only) match the
same possibilities as their corresponding normal (<firstterm>greedy</>)
counterparts, but prefer the smallest number rather than the largest
number of matches.
See <xref linkend="posix-matching-rules"> for more detail.
</para>
<note>
<para>
A quantifier cannot immediately follow another quantifier.
A quantifier cannot
begin an expression or subexpression or follow
<literal>^</literal> or <literal>|</literal>.
</para>
</note>
<table id="posix-constraints-table">
<title>Regular Expression Constraints</title>
<tgroup cols="2">
<thead>
<row>
<entry>Constraint</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry> <literal>^</> </entry>
<entry> matches at the beginning of the string </entry>
</row>
<row>
<entry> <literal>$</> </entry>
<entry> matches at the end of the string </entry>
</row>
<row>
<entry> <literal>(?=</><replaceable>re</><literal>)</> </entry>
<entry> <firstterm>positive lookahead</> matches at any point
where a substring matching <replaceable>re</> begins
(AREs only) </entry>
</row>
<row>
<entry> <literal>(?!</><replaceable>re</><literal>)</> </entry>
<entry> <firstterm>negative lookahead</> matches at any point
where no substring matching <replaceable>re</> begins
(AREs only) </entry>
</row>
</tbody>
</tgroup>
</table>
<para>
Lookahead constraints may not contain <firstterm>back references</>
(see <xref linkend="posix-escape-sequences">),
and all parentheses within them are considered non-capturing.
</para>
</sect3>
<sect3 id="posix-bracket-expressions">
<title>Bracket Expressions</title>
<para>
A <firstterm>bracket expression</firstterm> is a list of
characters enclosed in <literal>[]</literal>. It normally matches
any single character from the list (but see below). If the list
begins with <literal>^</literal>, it matches any single character
<emphasis>not</> from the rest of the list.
If two characters
in the list are separated by <literal>-</literal>, this is
shorthand for the full range of characters between those two
(inclusive) in the collating sequence,
e.g. <literal>[0-9]</literal> in <acronym>ASCII</acronym> matches
any decimal digit. It is illegal for two ranges to share an
endpoint, e.g. <literal>a-c-e</literal>. Ranges are very
collating-sequence-dependent, so portable programs should avoid
relying on them.
</para>
<para>
To include a literal <literal>]</literal> in the list, make it the
first character (following a possible <literal>^</literal>). To
include a literal <literal>-</literal>, make it the first or last
character, or the second endpoint of a range. To use a literal
<literal>-</literal> as the first endpoint of a range, enclose it
in <literal>[.</literal> and <literal>.]</literal> to make it a
collating element (see below). With the exception of these characters,
some combinations using <literal>[</literal>
(see next paragraphs), and escapes (AREs only), all other special
characters lose their special significance within a bracket expression.
In particular, <literal>\</literal> is not special when following
ERE or BRE rules, though it is special (as introducing an escape)
in AREs.
</para>
<para>
Within a bracket expression, a collating element (a character, a
multiple-character sequence that collates as if it were a single
character, or a collating-sequence name for either) enclosed in
<literal>[.</literal> and <literal>.]</literal> stands for the
sequence of characters of that collating element. The sequence is
a single element of the bracket expression's list. A bracket
expression containing a multiple-character collating element can thus
match more than one character, e.g. if the collating sequence
includes a <literal>ch</literal> collating element, then the RE
<literal>[[.ch.]]*c</literal> matches the first five characters of
<literal>chchcc</literal>.
</para>
<note>
<para>
<productname>PostgreSQL</> currently has no multi-character collating
elements. This information describes possible future behavior.
</para>
</note>
<para>
Within a bracket expression, a collating element enclosed in
<literal>[=</literal> and <literal>=]</literal> is an equivalence
class, standing for the sequences of characters of all collating
elements equivalent to that one, including itself. (If there are
no other equivalent collating elements, the treatment is as if the
enclosing delimiters were <literal>[.</literal> and
<literal>.]</literal>.) For example, if <literal>o</literal> and
<literal>^</literal> are the members of an equivalence class, then
<literal>[[=o=]]</literal>, <literal>[[=^=]]</literal>, and
<literal>[o^]</literal> are all synonymous. An equivalence class
may not be an endpoint of a range.
</para>
<para>
Within a bracket expression, the name of a character class
enclosed in <literal>[:</literal> and <literal>:]</literal> stands
for the list of all characters belonging to that class. Standard
character class names are: <literal>alnum</literal>,
<literal>alpha</literal>, <literal>blank</literal>,
<literal>cntrl</literal>, <literal>digit</literal>,
<literal>graph</literal>, <literal>lower</literal>,
<literal>print</literal>, <literal>punct</literal>,
<literal>space</literal>, <literal>upper</literal>,
<literal>xdigit</literal>. These stand for the character classes
defined in
<citerefentry><refentrytitle>ctype</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
A locale may provide others. A character class may not be used as
an endpoint of a range.
</para>
<para>
There are two special cases of bracket expressions: the bracket
expressions <literal>[[:&lt;:]]</literal> and
<literal>[[:&gt;:]]</literal> are constraints,
matching empty strings at the beginning
and end of a word respectively. A word is defined as a sequence
of word characters that is neither preceded nor followed by word
characters. A word character is an <literal>alnum</> character (as
defined by
<citerefentry><refentrytitle>ctype</refentrytitle><manvolnum>3</manvolnum></citerefentry>)
or an underscore. This is an extension, compatible with but not
specified by <acronym>POSIX</acronym> 1003.2, and should be used with
caution in software intended to be portable to other systems.
The constraint escapes described below are usually preferable (they
are no more standard, but are certainly easier to type).
</para>
</sect3>
<sect3 id="posix-escape-sequences">
<title>Regular Expression Escapes</title>
<para>
<firstterm>Escapes</> are special sequences beginning with <literal>\</>
followed by an alphanumeric character. Escapes come in several varieties:
character entry, class shorthands, constraint escapes, and back references.
A <literal>\</> followed by an alphanumeric character but not constituting
a valid escape is illegal in AREs.
In EREs, there are no escapes: outside a bracket expression,
a <literal>\</> followed by an alphanumeric character merely stands for
that character as an ordinary character, and inside a bracket expression,
<literal>\</> is an ordinary character.
(The latter is the one actual incompatibility between EREs and AREs.)
</para>
<para>
<firstterm>Character-entry escapes</> exist to make it easier to specify
non-printing and otherwise inconvenient characters in REs. They are
shown in <xref linkend="posix-character-entry-escapes-table">.
</para>
<para>
<firstterm>Class-shorthand escapes</> provide shorthands for certain
commonly-used character classes. They are
shown in <xref linkend="posix-class-shorthand-escapes-table">.
</para>
<para>
A <firstterm>constraint escape</> is a constraint,
matching the empty string if specific conditions are met,
written as an escape. They are
shown in <xref linkend="posix-constraint-escapes-table">.
</para>
<para>
A <firstterm>back reference</> (<literal>\</><replaceable>n</>) matches the
same string matched by the previous parenthesized subexpression specified
by the number <replaceable>n</>
(see <xref linkend="posix-constraint-backref-table">). For example,
<literal>([bc])\1</> matches <literal>bb</> or <literal>cc</>
but not <literal>bc</> or <literal>cb</>.
The subexpression must entirely precede the back reference in the RE.
Subexpressions are numbered in the order of their leading parentheses.
Non-capturing parentheses do not define subexpressions.
</para>
<note>
<para>
Keep in mind that an escape's leading <literal>\</> will need to be
doubled when entering the pattern as an SQL string constant.
</para>
</note>
<table id="posix-character-entry-escapes-table">
<title>Regular Expression Character-Entry Escapes</title>
<tgroup cols="2">
<thead>
<row>
<entry>Escape</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry> <literal>\a</> </entry>
<entry> alert (bell) character, as in C </entry>
</row>
<row>
<entry> <literal>\b</> </entry>
<entry> backspace, as in C </entry>
</row>
<row>
<entry> <literal>\B</> </entry>
<entry> synonym for <literal>\</> to help reduce the need for backslash
doubling </entry>
</row>
<row>
<entry> <literal>\c</><replaceable>X</> </entry>
<entry> (where <replaceable>X</> is any character) the character whose
low-order 5 bits are the same as those of
<replaceable>X</>, and whose other bits are all zero </entry>
</row>
<row>
<entry> <literal>\e</> </entry>
<entry> the character whose collating-sequence name
is <literal>ESC</>,
or failing that, the character with octal value 033 </entry>
</row>
<row>
<entry> <literal>\f</> </entry>
<entry> formfeed, as in C </entry>
</row>
<row>
<entry> <literal>\n</> </entry>
<entry> newline, as in C </entry>
</row>
<row>
<entry> <literal>\r</> </entry>
<entry> carriage return, as in C </entry>
</row>
<row>
<entry> <literal>\t</> </entry>
<entry> horizontal tab, as in C </entry>
</row>
<row>
<entry> <literal>\u</><replaceable>wxyz</> </entry>
<entry> (where <replaceable>wxyz</> is exactly four hexadecimal digits)
the Unicode character <literal>U+</><replaceable>wxyz</>
in the local byte ordering </entry>
</row>
<row>
<entry> <literal>\U</><replaceable>stuvwxyz</> </entry>
<entry> (where <replaceable>stuvwxyz</> is exactly eight hexadecimal
digits)
reserved for a somewhat-hypothetical Unicode extension to 32 bits
</entry>
</row>
<row>
<entry> <literal>\v</> </entry>
<entry> vertical tab, as in C </entry>
</row>
<row>
<entry> <literal>\x</><replaceable>hhh</> </entry>
<entry> (where <replaceable>hhh</> is any sequence of hexadecimal
digits)
the character whose hexadecimal value is
<literal>0x</><replaceable>hhh</>
(a single character no matter how many hexadecimal digits are used)
</entry>
</row>
<row>
<entry> <literal>\0</> </entry>
<entry> the character whose value is <literal>0</> </entry>
</row>
<row>
<entry> <literal>\</><replaceable>xy</> </entry>
<entry> (where <replaceable>xy</> is exactly two octal digits,
and is not a <firstterm>back reference</>)
the character whose octal value is
<literal>0</><replaceable>xy</> </entry>
</row>
<row>
<entry> <literal>\</><replaceable>xyz</> </entry>
<entry> (where <replaceable>xyz</> is exactly three octal digits,
and is not a <firstterm>back reference</>)
the character whose octal value is
<literal>0</><replaceable>xyz</> </entry>
</row>
</tbody>
</tgroup>
</table>
<para>
Hexadecimal digits are <literal>0</>-<literal>9</>,
<literal>a</>-<literal>f</>, and <literal>A</>-<literal>F</>.
Octal digits are <literal>0</>-<literal>7</>.
</para>
<para>
The character-entry escapes are always taken as ordinary characters.
For example, <literal>\135</> is <literal>]</> in ASCII, but
<literal>\135</> does not terminate a bracket expression.
</para>
<table id="posix-class-shorthand-escapes-table">
<title>Regular Expression Class-Shorthand Escapes</title>
<tgroup cols="2">
<thead>
<row>
<entry>Escape</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry> <literal>\d</> </entry>
<entry> <literal>[[:digit:]]</> </entry>
</row>
<row>
<entry> <literal>\s</> </entry>
<entry> <literal>[[:space:]]</> </entry>
</row>
<row>
<entry> <literal>\w</> </entry>
<entry> <literal>[[:alnum:]_]</>
(note underscore is included) </entry>
</row>
<row>
<entry> <literal>\D</> </entry>
<entry> <literal>[^[:digit:]]</> </entry>
</row>
<row>
<entry> <literal>\S</> </entry>
<entry> <literal>[^[:space:]]</> </entry>
</row>
<row>
<entry> <literal>\W</> </entry>
<entry> <literal>[^[:alnum:]_]</>
(note underscore is included) </entry>
</row>
</tbody>
</tgroup>
</table>
<para>
Within bracket expressions, <literal>\d</>, <literal>\s</>,
and <literal>\w</> lose their outer brackets,
and <literal>\D</>, <literal>\S</>, and <literal>\W</> are illegal.
(So, for example, <literal>[a-c\d]</> is equivalent to
<literal>[a-c[:digit:]]</>.
Also, <literal>[a-c\D]</>, which is equivalent to
<literal>[a-c^[:digit:]]</>, is illegal.)
</para>
<table id="posix-constraint-escapes-table">
<title>Regular Expression Constraint Escapes</title>
<tgroup cols="2">
<thead>
<row>
<entry>Escape</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry> <literal>\A</> </entry>
<entry> matches only at the beginning of the string
(see <xref linkend="posix-matching-rules"> for how this differs from
<literal>^</>) </entry>
</row>
<row>
<entry> <literal>\m</> </entry>
<entry> matches only at the beginning of a word </entry>
</row>
<row>
<entry> <literal>\M</> </entry>
<entry> matches only at the end of a word </entry>
</row>
<row>
<entry> <literal>\y</> </entry>
<entry> matches only at the beginning or end of a word </entry>
</row>
<row>
<entry> <literal>\Y</> </entry>
<entry> matches only at a point that is not the beginning or end of a
word </entry>
</row>
<row>
<entry> <literal>\Z</> </entry>
<entry> matches only at the end of the string
(see <xref linkend="posix-matching-rules"> for how this differs from
<literal>$</>) </entry>
</row>
</tbody>
</tgroup>
</table>
<para>
A word is defined as in the specification of
<literal>[[:&lt;:]]</> and <literal>[[:&gt;:]]</> above.
Constraint escapes are illegal within bracket expressions.
</para>
<table id="posix-constraint-backref-table">
<title>Regular Expression Back References</title>
<tgroup cols="2">
<thead>
<row>
<entry>Escape</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry> <literal>\</><replaceable>m</> </entry>
<entry> (where <replaceable>m</> is a nonzero digit)
a back reference to the <replaceable>m</>'th subexpression </entry>
</row>
<row>
<entry> <literal>\</><replaceable>mnn</> </entry>
<entry> (where <replaceable>m</> is a nonzero digit, and
<replaceable>nn</> is some more digits, and the decimal value
<replaceable>mnn</> is not greater than the number of closing capturing
parentheses seen so far)
a back reference to the <replaceable>mnn</>'th subexpression </entry>
</row>
</tbody>
</tgroup>
</table>
<note>
<para>
There is an inherent historical ambiguity between octal character-entry
escapes and back references, which is resolved by heuristics,
as hinted at above.
A leading zero always indicates an octal escape.
A single non-zero digit, not followed by another digit,
is always taken as a back reference.
A multi-digit sequence not starting with a zero is taken as a back
reference if it comes after a suitable subexpression
(i.e. the number is in the legal range for a back reference),
and otherwise is taken as octal.
</para>
</note>
</sect3>
<sect3 id="posix-metasyntax">
<title>Regular Expression Metasyntax</title>
<para>
In addition to the main syntax described above, there are some special
forms and miscellaneous syntactic facilities available.
</para>
<para>
Normally the flavor of RE being used is determined by
<varname>REGEX_FLAVOR</>.
However, this can be overridden by a <firstterm>director</> prefix.
If an RE of any flavor begins with <literal>***:</>,
the rest of the RE is taken as an ARE.
If an RE of any flavor begins with <literal>***=</>,
the rest of the RE is taken to be a literal string,
with all characters considered ordinary characters.
</para>
<para>
An ARE may begin with <firstterm>embedded options</>:
a sequence <literal>(?</><replaceable>xyz</><literal>)</>
(where <replaceable>xyz</> is one or more alphabetic characters)
specifies options affecting the rest of the RE.
These options override any previously determined options (including
both the RE flavor and case sensitivity).
The available option letters are
shown in <xref linkend="posix-embedded-options-table">.
</para>
<table id="posix-embedded-options-table">
<title>ARE Embedded-Option Letters</title>
<tgroup cols="2">
<thead>
<row>
<entry>Option</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry> <literal>b</> </entry>
<entry> rest of RE is a BRE </entry>
</row>
<row>
<entry> <literal>c</> </entry>
<entry> case-sensitive matching (overrides operator type) </entry>
</row>
<row>
<entry> <literal>e</> </entry>
<entry> rest of RE is an ERE </entry>
</row>
<row>
<entry> <literal>i</> </entry>
<entry> case-insensitive matching (see
<xref linkend="posix-matching-rules">) (overrides operator type) </entry>
</row>
<row>
<entry> <literal>m</> </entry>
<entry> historical synonym for <literal>n</> </entry>
</row>
<row>
<entry> <literal>n</> </entry>
<entry> newline-sensitive matching (see
<xref linkend="posix-matching-rules">) </entry>
</row>
<row>
<entry> <literal>p</> </entry>
<entry> partial newline-sensitive matching (see
<xref linkend="posix-matching-rules">) </entry>
</row>
<row>
<entry> <literal>q</> </entry>
<entry> rest of RE is a literal (<quote>quoted</>) string, all ordinary
characters </entry>
</row>
<row>
<entry> <literal>s</> </entry>
<entry> non-newline-sensitive matching (default) </entry>
</row>
<row>
<entry> <literal>t</> </entry>
<entry> tight syntax (default; see below) </entry>
</row>
<row>
<entry> <literal>w</> </entry>
<entry> inverse partial newline-sensitive (<quote>weird</>) matching
(see <xref linkend="posix-matching-rules">) </entry>
</row>
<row>
<entry> <literal>x</> </entry>
<entry> expanded syntax (see below) </entry>
</row>
</tbody>
</tgroup>
</table>
<para>
Embedded options take effect at the <literal>)</> terminating the sequence.
They are available only at the start of an ARE,
and may not be used later within it.
</para>
<para>
In addition to the usual (<firstterm>tight</>) RE syntax, in which all
characters are significant, there is an <firstterm>expanded</> syntax,
available by specifying the embedded <literal>x</> option.
In the expanded syntax,
white-space characters in the RE are ignored, as are
all characters between a <literal>#</>
and the following newline (or the end of the RE). This
permits paragraphing and commenting a complex RE.
There are three exceptions to that basic rule:
<itemizedlist>
<listitem>
<para>
a white-space character or <literal>#</> preceded by <literal>\</> is
retained
</para>
</listitem>
<listitem>
<para>
white space or <literal>#</> within a bracket expression is retained
</para>
</listitem>
<listitem>
<para>
white space and comments are illegal within multi-character symbols,
like the ARE <literal>(?:</> or the BRE <literal>\(</>
</para>
</listitem>
</itemizedlist>
Expanded-syntax white-space characters are blank, tab, newline, and
any character that belongs to the <replaceable>space</> character class.
</para>
<para>
Finally, in an ARE, outside bracket expressions, the sequence
<literal>(?#</><replaceable>ttt</><literal>)</>
(where <replaceable>ttt</> is any text not containing a <literal>)</>)
is a comment, completely ignored.
Again, this is not allowed between the characters of
multi-character symbols, like <literal>(?:</>.
Such comments are more a historical artifact than a useful facility,
and their use is deprecated; use the expanded syntax instead.
</para>
<para>
<emphasis>None</> of these metasyntax extensions is available if
an initial <literal>***=</> director
has specified that the user's input be treated as a literal string
rather than as an RE.
</para>
</sect3>
<sect3 id="posix-matching-rules">
<title>Regular Expression Matching Rules</title>
<para>
In the event that an RE could match more than one substring of a given
string, the RE matches the one starting earliest in the string.
If the RE could match more than one substring starting at that point,
its choice is determined by its <firstterm>preference</>:
either the longest substring, or the shortest.
</para>
<para>
Most atoms, and all constraints, have no preference.
A parenthesized RE has the same preference (possibly none) as the RE.
A quantified atom with quantifier
<literal>{</><replaceable>m</><literal>}</>
or
<literal>{</><replaceable>m</><literal>}?</>
has the same preference (possibly none) as the atom itself.
A quantified atom with other normal quantifiers (including
<literal>{</><replaceable>m</><literal>,</><replaceable>n</><literal>}</>
with <replaceable>m</> equal to <replaceable>n</>)
prefers longest match.
A quantified atom with other non-greedy quantifiers (including
<literal>{</><replaceable>m</><literal>,</><replaceable>n</><literal>}?</>
with <replaceable>m</> equal to <replaceable>n</>)
prefers shortest match.
A branch has the same preference as the first quantified atom in it
which has a preference.
An RE consisting of two or more branches connected by the
<literal>|</> operator prefers longest match.
</para>
<para>
Subject to the constraints imposed by the rules for matching the whole RE,
subexpressions also match the longest or shortest possible substrings,
based on their preferences,
with subexpressions starting earlier in the RE taking priority over
ones starting later.
Note that outer subexpressions thus take priority over
their component subexpressions.
</para>
<para>
The quantifiers <literal>{1,1}</> and <literal>{1,1}?</>
can be used to force longest and shortest preference, respectively,
on a subexpression or a whole RE.
</para>
<para>
Match lengths are measured in characters, not collating elements.
An empty string is considered longer than no match at all.
For example:
<literal>bb*</>
matches the three middle characters of <literal>abbbc</>;
<literal>(week|wee)(night|knights)</>
matches all ten characters of <literal>weeknights</>;
when <literal>(.*).*</>
is matched against <literal>abc</> the parenthesized subexpression
matches all three characters; and when
<literal>(a*)*</> is matched against <literal>bc</>
both the whole RE and the parenthesized
subexpression match an empty string.
</para>
<para>
If case-independent matching is specified,
the effect is much as if all case distinctions had vanished from the
alphabet.
When an alphabetic that exists in multiple cases appears as an
ordinary character outside a bracket expression, it is effectively
transformed into a bracket expression containing both cases,
e.g. <literal>x</> becomes <literal>[xX]</>.
When it appears inside a bracket expression, all case counterparts
of it are added to the bracket expression, e.g.
<literal>[x]</> becomes <literal>[xX]</>
and <literal>[^x]</> becomes <literal>[^xX]</>.
</para>
<para>
If newline-sensitive matching is specified, <literal>.</>
and bracket expressions using <literal>^</>
will never match the newline character
(so that matches will never cross newlines unless the RE
explicitly arranges it)
and <literal>^</>and <literal>$</>
will match the empty string after and before a newline
respectively, in addition to matching at beginning and end of string
respectively.
But the ARE escapes <literal>\A</> and <literal>\Z</>
continue to match beginning or end of string <emphasis>only</>.
</para>
<para>
If partial newline-sensitive matching is specified,
this affects <literal>.</> and bracket expressions
as with newline-sensitive matching, but not <literal>^</>
and <literal>$</>.
</para>
<para>
If inverse partial newline-sensitive matching is specified,
this affects <literal>^</> and <literal>$</>
as with newline-sensitive matching, but not <literal>.</>
and bracket expressions.
This isn't very useful but is provided for symmetry.
</para>
</sect3>
<sect3 id="posix-limits-compatibility">
<title>Limits and Compatibility</title>
<para>
No particular limit is imposed on the length of REs in this
implementation. However,
programs intended to be highly portable should not employ REs longer
than 256 bytes,
as a POSIX-compliant implementation can refuse to accept such REs.
</para>
<para>
The only feature of AREs that is actually incompatible with
POSIX EREs is that <literal>\</> does not lose its special
significance inside bracket expressions.
All other ARE features use syntax which is illegal or has
undefined or unspecified effects in POSIX EREs;
the <literal>***</> syntax of directors likewise is outside the POSIX
syntax for both BREs and EREs.
</para>
<para>
Many of the ARE extensions are borrowed from Perl, but some have
been changed to clean them up, and a few Perl extensions are not present.
Incompatibilities of note include <literal>\b</>, <literal>\B</>,
the lack of special treatment for a trailing newline,
the addition of complemented bracket expressions to the things
affected by newline-sensitive matching,
the restrictions on parentheses and back references in lookahead
constraints, and the longest/shortest-match (rather than first-match)
matching semantics.
</para>
<para>
Two significant incompatibilities exist between AREs and the ERE syntax
recognized by pre-7.4 releases of <productname>PostgreSQL</>:
<itemizedlist>
<listitem>
<para>
In AREs, <literal>\</> followed by an alphanumeric character is either
an escape or an error, while in previous releases, it was just another
way of writing the alphanumeric.
This should not be much of a problem because there was no reason to
write such a sequence in earlier releases.
</para>
</listitem>
<listitem>
<para>
In AREs, <literal>\</> remains a special character within
<literal>[]</>, so a literal <literal>\</> within a bracket
expression must be written <literal>\\</>.
</para>
</listitem>
</itemizedlist>
While these differences are unlikely to create a problem for most
applications, you can avoid them if necessary by
setting <varname>REGEX_FLAVOR</> to <literal>extended</>.
</para>
</sect3>
<sect3 id="posix-basic-regexes">
<title>Basic Regular Expressions</title>
<para>
BREs differ from EREs in several respects.
<literal>|</>, <literal>+</>, and <literal>?</>
are ordinary characters and there is no equivalent
for their functionality.
The delimiters for bounds are
<literal>\{</> and <literal>\}</>,
with <literal>{</> and <literal>}</>
by themselves ordinary characters.
The parentheses for nested subexpressions are
<literal>\(</> and <literal>\)</>,
with <literal>(</> and <literal>)</> by themselves ordinary characters.
<literal>^</> is an ordinary character except at the beginning of the
RE or the beginning of a parenthesized subexpression,
<literal>$</> is an ordinary character except at the end of the
RE or the end of a parenthesized subexpression,
and <literal>*</> is an ordinary character if it appears at the beginning
of the RE or the beginning of a parenthesized subexpression
(after a possible leading <literal>^</>).
Finally, single-digit back references are available, and
<literal>\&lt;</> and <literal>\&gt;</>
are synonyms for
<literal>[[:&lt;:]]</> and <literal>[[:&gt;:]]</>
respectively; no other escapes are available.
</para>
</sect3>
<!-- end re_syntax.n man page -->
</sect2>
</sect1>
<sect1 id="functions-formatting">
<title>Data Type Formatting Functions</title>
<indexterm zone="functions-formatting">
<primary>formatting</primary>
</indexterm>
<para>
The <productname>PostgreSQL</productname> formatting functions
provide a powerful set of tools for converting various data types
(date/time, integer, floating point, numeric) to formatted strings
and for converting from formatted strings to specific data types.
<xref linkend="functions-formatting-table"> lists them.
These functions all follow a common calling convention: the first
argument is the value to be formatted and the second argument is a
template that defines the output or input format.
</para>
<table id="functions-formatting-table">
<title>Formatting Functions</title>
<tgroup cols="4">
<thead>
<row>
<entry>Function</entry>
<entry>Returns</entry>
<entry>Description</entry>
<entry>Example</entry>
</row>
</thead>
<tbody>
<row>
<entry><function>to_char</function>(<type>timestamp</type>, <type>text</type>)</entry>
<entry><type>text</type></entry>
<entry>convert time stamp to string</entry>
<entry><literal>to_char(timestamp 'now','HH12:MI:SS')</literal></entry>
</row>
<row>
<entry><function>to_char</function>(<type>interval</type>, <type>text</type>)</entry>
<entry><type>text</type></entry>
<entry>convert interval to string</entry>
<entry><literal>to_char(interval '15h 2m 12s','HH24:MI:SS')</literal></entry>
</row>
<row>
<entry><function>to_char</function>(<type>int</type>, <type>text</type>)</entry>
<entry><type>text</type></entry>
<entry>convert integer to string</entry>
<entry><literal>to_char(125, '999')</literal></entry>
</row>
<row>
<entry><function>to_char</function>(<type>double precision</type>,
<type>text</type>)</entry>
<entry><type>text</type></entry>
<entry>convert real/double precision to string</entry>
<entry><literal>to_char(125.8, '999D9')</literal></entry>
</row>
<row>
<entry><function>to_char</function>(<type>numeric</type>, <type>text</type>)</entry>
<entry><type>text</type></entry>
<entry>convert numeric to string</entry>
<entry><literal>to_char(numeric '-125.8', '999D99S')</literal></entry>
</row>
<row>
<entry><function>to_date</function>(<type>text</type>, <type>text</type>)</entry>
<entry><type>date</type></entry>
<entry>convert string to date</entry>
<entry><literal>to_date('05 Dec 2000', 'DD Mon YYYY')</literal></entry>
</row>
<row>
<entry><function>to_timestamp</function>(<type>text</type>, <type>text</type>)</entry>
<entry><type>timestamp</type></entry>
<entry>convert string to time stamp</entry>
<entry><literal>to_timestamp('05 Dec 2000', 'DD Mon YYYY')</literal></entry>
</row>
<row>
<entry><function>to_number</function>(<type>text</type>, <type>text</type>)</entry>
<entry><type>numeric</type></entry>
<entry>convert string to numeric</entry>
<entry><literal>to_number('12,454.8-', '99G999D9S')</literal></entry>
</row>
</tbody>
</tgroup>
</table>
<para>
In an output template string, there are certain patterns that are
recognized and replaced with appropriately-formatted data from the value
to be formatted. Any text that is not a template pattern is simply
copied verbatim. Similarly, in an input template string, template patterns
identify the parts of the input data string to be looked at and the
values to be found there.
</para>
<para>
<xref linkend="functions-formatting-datetime-table"> shows the
template patterns available for formatting date and time values.
</para>
<table id="functions-formatting-datetime-table">
<title>Template patterns for date/time conversions</title>
<tgroup cols="2">
<thead>
<row>
<entry>Pattern</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry><literal>HH</literal></entry>
<entry>hour of day (01-12)</entry>
</row>
<row>
<entry><literal>HH12</literal></entry>
<entry>hour of day (01-12)</entry>
</row>
<row>
<entry><literal>HH24</literal></entry>
<entry>hour of day (00-23)</entry>
</row>
<row>
<entry><literal>MI</literal></entry>
<entry>minute (00-59)</entry>
</row>
<row>
<entry><literal>SS</literal></entry>
<entry>second (00-59)</entry>
</row>
<row>
<entry><literal>MS</literal></entry>
<entry>millisecond (000-999)</entry>
</row>
<row>
<entry><literal>US</literal></entry>
<entry>microsecond (000000-999999)</entry>
</row>
<row>
<entry><literal>SSSS</literal></entry>
<entry>seconds past midnight (0-86399)</entry>
</row>
<row>
<entry><literal>AM</literal> or <literal>A.M.</literal> or
<literal>PM</literal> or <literal>P.M.</literal></entry>
<entry>meridian indicator (upper case)</entry>
</row>
<row>
<entry><literal>am</literal> or <literal>a.m.</literal> or
<literal>pm</literal> or <literal>p.m.</literal></entry>
<entry>meridian indicator (lower case)</entry>
</row>
<row>
<entry><literal>Y,YYY</literal></entry>
<entry>year (4 and more digits) with comma</entry>
</row>
<row>
<entry><literal>YYYY</literal></entry>
<entry>year (4 and more digits)</entry>
</row>
<row>
<entry><literal>YYY</literal></entry>
<entry>last 3 digits of year</entry>
</row>
<row>
<entry><literal>YY</literal></entry>
<entry>last 2 digits of year</entry>
</row>
<row>
<entry><literal>Y</literal></entry>
<entry>last digit of year</entry>
</row>
<row>
<entry><literal>BC</literal> or <literal>B.C.</literal> or
<literal>AD</literal> or <literal>A.D.</literal></entry>
<entry>era indicator (upper case)</entry>
</row>
<row>
<entry><literal>bc</literal> or <literal>b.c.</literal> or
<literal>ad</literal> or <literal>a.d.</literal></entry>
<entry>era indicator (lower case)</entry>
</row>
<row>
<entry><literal>MONTH</literal></entry>
<entry>full upper case month name (blank-padded to 9 chars)</entry>
</row>
<row>
<entry><literal>Month</literal></entry>
<entry>full mixed case month name (blank-padded to 9 chars)</entry>
</row>
<row>
<entry><literal>month</literal></entry>
<entry>full lower case month name (blank-padded to 9 chars)</entry>
</row>
<row>
<entry><literal>MON</literal></entry>
<entry>abbreviated upper case month name (3 chars)</entry>
</row>
<row>
<entry><literal>Mon</literal></entry>
<entry>abbreviated mixed case month name (3 chars)</entry>
</row>
<row>
<entry><literal>mon</literal></entry>
<entry>abbreviated lower case month name (3 chars)</entry>
</row>
<row>
<entry><literal>MM</literal></entry>
<entry>month number (01-12)</entry>
</row>
<row>
<entry><literal>DAY</literal></entry>
<entry>full upper case day name (blank-padded to 9 chars)</entry>
</row>
<row>
<entry><literal>Day</literal></entry>
<entry>full mixed case day name (blank-padded to 9 chars)</entry>
</row>
<row>
<entry><literal>day</literal></entry>
<entry>full lower case day name (blank-padded to 9 chars)</entry>
</row>
<row>
<entry><literal>DY</literal></entry>
<entry>abbreviated upper case day name (3 chars)</entry>
</row>
<row>
<entry><literal>Dy</literal></entry>
<entry>abbreviated mixed case day name (3 chars)</entry>
</row>
<row>
<entry><literal>dy</literal></entry>
<entry>abbreviated lower case day name (3 chars)</entry>
</row>
<row>
<entry><literal>DDD</literal></entry>
<entry>day of year (001-366)</entry>
</row>
<row>
<entry><literal>DD</literal></entry>
<entry>day of month (01-31)</entry>
</row>
<row>
<entry><literal>D</literal></entry>
<entry>day of week (1-7; SUN=1)</entry>
</row>
<row>
<entry><literal>W</literal></entry>
<entry>week of month (1-5) where first week start on the first day of the month</entry>
</row>
<row>
<entry><literal>WW</literal></entry>
<entry>week number of year (1-53) where first week start on the first day of the year</entry>
</row>
<row>
<entry><literal>IW</literal></entry>
<entry>ISO week number of year (The first Thursday of the new year is in week 1.)</entry>
</row>
<row>
<entry><literal>CC</literal></entry>
<entry>century (2 digits)</entry>
</row>
<row>
<entry><literal>J</literal></entry>
<entry>Julian Day (days since January 1, 4712 BC)</entry>
</row>
<row>
<entry><literal>Q</literal></entry>
<entry>quarter</entry>
</row>
<row>
<entry><literal>RM</literal></entry>
<entry>month in Roman Numerals (I-XII; I=January) - upper case</entry>
</row>
<row>
<entry><literal>rm</literal></entry>
<entry>month in Roman Numerals (I-XII; I=January) - lower case</entry>
</row>
<row>
<entry><literal>TZ</literal></entry>
<entry>time-zone name - upper case</entry>
</row>
<row>
<entry><literal>tz</literal></entry>
<entry>time-zone name - lower case</entry>
</row>
</tbody>
</tgroup>
</table>
<para>
Certain modifiers may be applied to any template pattern to alter its
behavior. For example, <quote><literal>FMMonth</literal></quote>
is the <quote><literal>Month</literal></quote> pattern with the
<quote><literal>FM</literal></quote> prefix.
<xref linkend="functions-formatting-datetimemod-table"> shows the
modifier patterns for date/time formatting.
</para>
<table id="functions-formatting-datetimemod-table">
<title>Template pattern modifiers for date/time conversions</title>
<tgroup cols="3">
<thead>
<row>
<entry>Modifier</entry>
<entry>Description</entry>
<entry>Example</entry>
</row>
</thead>
<tbody>
<row>
<entry><literal>FM</literal> prefix</entry>
<entry>fill mode (suppress padding blanks and zeroes)</entry>
<entry><literal>FMMonth</literal></entry>
</row>
<row>
<entry><literal>TH</literal> suffix</entry>
<entry>add upper-case ordinal number suffix</entry>
<entry><literal>DDTH</literal></entry>
</row>
<row>
<entry><literal>th</literal> suffix</entry>
<entry>add lower-case ordinal number suffix</entry>
<entry><literal>DDth</literal></entry>
</row>
<row>
<entry><literal>FX</literal> prefix</entry>
<entry>fixed format global option (see usage notes)</entry>
<entry><literal>FX Month DD Day</literal></entry>
</row>
<row>
<entry><literal>SP</literal> suffix</entry>
<entry>spell mode (not yet implemented)</entry>
<entry><literal>DDSP</literal></entry>
</row>
</tbody>
</tgroup>
</table>
<para>
Usage notes for the date/time formatting:
<itemizedlist>
<listitem>
<para>
<literal>FM</literal> suppresses leading zeroes and trailing blanks
that would otherwise be added to make the output of a pattern be
fixed-width.
</para>
</listitem>
<listitem>
<para>
<function>to_timestamp</function> and <function>to_date</function>
skip multiple blank spaces in the input string if the <literal>FX</literal> option
is not used. <literal>FX</literal> must be specified as the first item
in the template; for example
<literal>to_timestamp('2000 JUN','YYYY MON')</literal> is right, but
<literal>to_timestamp('2000 JUN','FXYYYY MON')</literal> returns an error,
because <function>to_timestamp</function> expects one blank space only.
</para>
</listitem>
<listitem>
<para>
If a backslash (<quote><literal>\</literal></quote>) is desired
in a string constant, a double backslash
(<quote><literal>\\</literal></quote>) must be entered; for
example <literal>'\\HH\\MI\\SS'</literal>. This is true for
any string constant in <productname>PostgreSQL</productname>.
</para>
</listitem>
<listitem>
<para>
Ordinary text is allowed in <function>to_char</function>
templates and will be output literally. You can put a substring
in double quotes to force it to be interpreted as literal text
even if it contains pattern keywords. For example, in
<literal>'"Hello Year "YYYY'</literal>, the <literal>YYYY</literal>
will be replaced by the year data, but the single <literal>Y</literal> in <quote>Year</quote>
will not be.
</para>
</listitem>
<listitem>
<para>
If you want to have a double quote in the output you must
precede it with a backslash, for example <literal>'\\"YYYY
Month\\"'</literal>. <!-- "" font-lock sanity :-) -->
</para>
</listitem>
<listitem>
<para>
<literal>YYYY</literal> conversion from string to <type>timestamp</type> or
<type>date</type> is restricted if you use a year with more than 4 digits. You must
use some non-digit character or template after <literal>YYYY</literal>,
otherwise the year is always interpreted as 4 digits. For example
(with year 20000):
<literal>to_date('200001131', 'YYYYMMDD')</literal> will be
interpreted as a 4-digit year; better is to use a non-digit
separator after the year, like
<literal>to_date('20000-1131', 'YYYY-MMDD')</literal> or
<literal>to_date('20000Nov31', 'YYYYMonDD')</literal>.
</para>
</listitem>
<listitem>
<para>
Millisecond <literal>MS</literal> and microsecond <literal>US</literal>
values in a conversion from string to time stamp are used as part of the
seconds after the decimal point. For example
<literal>to_timestamp('12:3', 'SS:MS')</literal> is not 3 milliseconds,
but 300, because the conversion counts it as 12 + 0.3.
This means for the format <literal>SS:MS</literal>, the input values
<literal>12:3</literal>, <literal>12:30</literal>, and <literal>12:300</literal> specify the
same number of milliseconds. To get three milliseconds, one must use
<literal>12:003</literal>, which the conversion counts as
12 + 0.003 = 12.003 seconds.
</para>
<para>
Here is a more
complex example:
<literal>to_timestamp('15:12:02.020.001230','HH:MI:SS.MS.US')</literal>
is 15 hours, 12 minutes, and 2 seconds + 20 milliseconds +
1230 microseconds = 2.021230 seconds.
</para>
</listitem>
</itemizedlist>
</para>
<para>
<xref linkend="functions-formatting-numeric-table"> shows the
template patterns available for formatting numeric values.
</para>
<table id="functions-formatting-numeric-table">
<title>Template patterns for numeric conversions</title>
<tgroup cols="2">
<thead>
<row>
<entry>Pattern</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry><literal>9</literal></entry>
<entry>value with the specified number of digits</entry>
</row>
<row>
<entry><literal>0</literal></entry>
<entry>value with leading zeros</entry>
</row>
<row>
<entry><literal>.</literal> (period)</entry>
<entry>decimal point</entry>
</row>
<row>
<entry><literal>,</literal> (comma)</entry>
<entry>group (thousand) separator</entry>
</row>
<row>
<entry><literal>PR</literal></entry>
<entry>negative value in angle brackets</entry>
</row>
<row>
<entry><literal>S</literal></entry>
<entry>negative value with minus sign (uses locale)</entry>
</row>
<row>
<entry><literal>L</literal></entry>
<entry>currency symbol (uses locale)</entry>
</row>
<row>
<entry><literal>D</literal></entry>
<entry>decimal point (uses locale)</entry>
</row>
<row>
<entry><literal>G</literal></entry>
<entry>group separator (uses locale)</entry>
</row>
<row>
<entry><literal>MI</literal></entry>
<entry>minus sign in specified position (if number &lt; 0)</entry>
</row>
<row>
<entry><literal>PL</literal></entry>
<entry>plus sign in specified position (if number &gt; 0)</entry>
</row>
<row>
<entry><literal>SG</literal></entry>
<entry>plus/minus sign in specified position</entry>
</row>
<row>
<entry><literal>RN</literal></entry>
<entry>roman numeral (input between 1 and 3999)</entry>
</row>
<row>
<entry><literal>TH</literal> or <literal>th</literal></entry>
<entry>convert to ordinal number</entry>
</row>
<row>
<entry><literal>V</literal></entry>
<entry>shift <replaceable>n</replaceable> digits (see
notes)</entry>
</row>
<row>
<entry><literal>EEEE</literal></entry>
<entry>scientific notation (not implemented yet)</entry>
</row>
</tbody>
</tgroup>
</table>
<para>
Usage notes for the numeric formatting:
<itemizedlist>
<listitem>
<para>
A sign formatted using <literal>SG</literal>, <literal>PL</literal>, or
<literal>MI</literal> is not an anchor in
the number; for example,
<literal>to_char(-12, 'S9999')</literal> produces <literal>' -12'</literal>,
but <literal>to_char(-12, 'MI9999')</literal> produces <literal>'- 12'</literal>.
The Oracle implementation does not allow the use of
<literal>MI</literal> ahead of <literal>9</literal>, but rather
requires that <literal>9</literal> precede
<literal>MI</literal>.
</para>
</listitem>
<listitem>
<para>
<literal>9</literal> specifies a value with the same number of
digits as there are <literal>9</literal>s. If a digit is
not available it outputs a space.
</para>
</listitem>
<listitem>
<para>
<literal>TH</literal> does not convert values less than zero
and does not convert decimal numbers.
</para>
</listitem>
<listitem>
<para>
<literal>PL</literal>, <literal>SG</literal>, and
<literal>TH</literal> are <productname>PostgreSQL</productname>
extensions.
</para>
</listitem>
<listitem>
<para>
<literal>V</literal> effectively
multiplies the input values by
<literal>10^<replaceable>n</replaceable></literal>, where
<replaceable>n</replaceable> is the number of digits following
<literal>V</literal>.
<function>to_char</function> does not support the use of
<literal>V</literal> combined with a decimal point.
(E.g., <literal>99.9V99</literal> is not allowed.)
</para>
</listitem>
</itemizedlist>
</para>
<para>
<xref linkend="functions-formatting-examples-table"> shows some
examples of the use of the <function>to_char</function> function.
</para>
<table id="functions-formatting-examples-table">
<title><function>to_char</function> Examples</title>
<tgroup cols="2">
<thead>
<row>
<entry>Input</entry>
<entry>Output</entry>
</row>
</thead>
<tbody>
<row>
<entry><literal>to_char(now(),'Day, DD HH12:MI:SS')</literal></entry>
<entry><literal>'Tuesday , 06 05:39:18'</literal></entry>
</row>
<row>
<entry><literal>to_char(now(),'FMDay, FMDD HH12:MI:SS')</literal></entry>
<entry><literal>'Tuesday, 6 05:39:18'</literal></entry>
</row>
<row>
<entry><literal>to_char(-0.1,'99.99')</literal></entry>
<entry><literal>' -.10'</literal></entry>
</row>
<row>
<entry><literal>to_char(-0.1,'FM9.99')</literal></entry>
<entry><literal>'-.1'</literal></entry>
</row>
<row>
<entry><literal>to_char(0.1,'0.9')</literal></entry>
<entry><literal>' 0.1'</literal></entry>
</row>
<row>
<entry><literal>to_char(12,'9990999.9')</literal></entry>
<entry><literal>' 0012.0'</literal></entry>
</row>
<row>
<entry><literal>to_char(12,'FM9990999.9')</literal></entry>
<entry><literal>'0012'</literal></entry>
</row>
<row>
<entry><literal>to_char(485,'999')</literal></entry>
<entry><literal>' 485'</literal></entry>
</row>
<row>
<entry><literal>to_char(-485,'999')</literal></entry>
<entry><literal>'-485'</literal></entry>
</row>
<row>
<entry><literal>to_char(485,'9 9 9')</literal></entry>
<entry><literal>' 4 8 5'</literal></entry>
</row>
<row>
<entry><literal>to_char(1485,'9,999')</literal></entry>
<entry><literal>' 1,485'</literal></entry>
</row>
<row>
<entry><literal>to_char(1485,'9G999')</literal></entry>
<entry><literal>' 1 485'</literal></entry>
</row>
<row>
<entry><literal>to_char(148.5,'999.999')</literal></entry>
<entry><literal>' 148.500'</literal></entry>
</row>
<row>
<entry><literal>to_char(148.5,'999D999')</literal></entry>
<entry><literal>' 148,500'</literal></entry>
</row>
<row>
<entry><literal>to_char(3148.5,'9G999D999')</literal></entry>
<entry><literal>' 3 148,500'</literal></entry>
</row>
<row>
<entry><literal>to_char(-485,'999S')</literal></entry>
<entry><literal>'485-'</literal></entry>
</row>
<row>
<entry><literal>to_char(-485,'999MI')</literal></entry>
<entry><literal>'485-'</literal></entry>
</row>
<row>
<entry><literal>to_char(485,'999MI')</literal></entry>
<entry><literal>'485'</literal></entry>
</row>
<row>
<entry><literal>to_char(485,'PL999')</literal></entry>
<entry><literal>'+485'</literal></entry>
</row>
<row>
<entry><literal>to_char(485,'SG999')</literal></entry>
<entry><literal>'+485'</literal></entry>
</row>
<row>
<entry><literal>to_char(-485,'SG999')</literal></entry>
<entry><literal>'-485'</literal></entry>
</row>
<row>
<entry><literal>to_char(-485,'9SG99')</literal></entry>
<entry><literal>'4-85'</literal></entry>
</row>
<row>
<entry><literal>to_char(-485,'999PR')</literal></entry>
<entry><literal>'&lt;485&gt;'</literal></entry>
</row>
<row>
<entry><literal>to_char(485,'L999')</literal></entry>
<entry><literal>'DM 485</literal></entry>
</row>
<row>
<entry><literal>to_char(485,'RN')</literal></entry>
<entry><literal>' CDLXXXV'</literal></entry>
</row>
<row>
<entry><literal>to_char(485,'FMRN')</literal></entry>
<entry><literal>'CDLXXXV'</literal></entry>
</row>
<row>
<entry><literal>to_char(5.2,'FMRN')</literal></entry>
<entry><literal>V</literal></entry>
</row>
<row>
<entry><literal>to_char(482,'999th')</literal></entry>
<entry><literal>' 482nd'</literal></entry>
</row>
<row>
<entry><literal>to_char(485, '"Good number:"999')</literal></entry>
<entry><literal>'Good number: 485'</literal></entry>
</row>
<row>
<entry><literal>to_char(485.8,'"Pre:"999" Post:" .999')</literal></entry>
<entry><literal>'Pre: 485 Post: .800'</literal></entry>
</row>
<row>
<entry><literal>to_char(12,'99V999')</literal></entry>
<entry><literal>' 12000'</literal></entry>
</row>
<row>
<entry><literal>to_char(12.4,'99V999')</literal></entry>
<entry><literal>' 12400'</literal></entry>
</row>
<row>
<entry><literal>to_char(12.45, '99V9')</literal></entry>
<entry><literal>' 125'</literal></entry>
</row>
</tbody>
</tgroup>
</table>
</sect1>
<sect1 id="functions-datetime">
<title>Date/Time Functions and Operators</title>
<para>
<xref linkend="functions-datetime-table"> shows the available
functions for date/time value processing, with details appearing in
the following subsections. <xref
linkend="operators-datetime-table"> illustrates the behaviors of
the basic arithmetic operators (<literal>+</literal>,
<literal>*</literal>, etc.). For formatting functions, refer to
<xref linkend="functions-formatting">. You should be familiar with
the background information on date/time data types (see <xref
linkend="datatype-datetime">).
</para>
<para>
All the functions and operators described below that take time or timestamp
inputs actually come in two variants: one that takes time or timestamp
with time zone, and one that takes time or timestamp without time zone.
For brevity, these variants are not shown separately.
</para>
<table id="operators-datetime-table">
<title>Date/Time Operators</title>
<tgroup cols="3">
<thead>
<row>
<entry>Name</entry>
<entry>Example</entry>
<entry>Result</entry>
</row>
</thead>
<tbody>
<row>
<entry> <literal>+</literal> </entry>
<entry><literal>timestamp '2001-09-28 01:00' + interval '23 hours'</literal></entry>
<entry><literal>timestamp '2001-09-29 00:00'</literal></entry>
</row>
<row>
<entry> <literal>+</literal> </entry>
<entry><literal>date '2001-09-28' + interval '1 hour'</literal></entry>
<entry><literal>timestamp '2001-09-28 01:00'</literal></entry>
</row>
<row>
<entry> <literal>+</literal> </entry>
<entry><literal>time '01:00' + interval '3 hours'</literal></entry>
<entry><literal>time '04:00'</literal></entry>
</row>
<row>
<entry> <literal>-</literal> </entry>
<entry><literal>timestamp '2001-09-28 23:00' - interval '23 hours'</literal></entry>
<entry><literal>timestamp '2001-09-28'</literal></entry>
</row>
<row>
<entry> <literal>-</literal> </entry>
<entry><literal>date '2001-09-28' - interval '1 hour'</literal></entry>
<entry><literal>timestamp '2001-09-27 23:00'</literal></entry>
</row>
<row>
<entry> <literal>-</literal> </entry>
<entry><literal>time '05:00' - interval '2 hours'</literal></entry>
<entry><literal>time '03:00'</literal></entry>
</row>
<row>
<entry> <literal>-</literal> </entry>
<entry><literal>interval '2 hours' - time '05:00'</literal></entry>
<entry><literal>time '03:00:00'</literal></entry>
</row>
<row>
<entry> <literal>*</literal> </entry>
<entry><literal>interval '1 hour' * int '3'</literal></entry>
<entry><literal>interval '03:00'</literal></entry>
</row>
<row>
<entry> <literal>/</literal> </entry>
<entry><literal>interval '1 hour' / int '3'</literal></entry>
<entry><literal>interval '00:20'</literal></entry>
</row>
</tbody>
</tgroup>
</table>
<table id="functions-datetime-table">
<title>Date/Time Functions</title>
<tgroup cols="5">
<thead>
<row>
<entry>Name</entry>
<entry>Return Type</entry>
<entry>Description</entry>
<entry>Example</entry>
<entry>Result</entry>
</row>
</thead>
<tbody>
<row>
<entry><function>age</function>(<type>timestamp</type>)</entry>
<entry><type>interval</type></entry>
<entry>Subtract from today</entry>
<entry><literal>age(timestamp '1957-06-13')</literal></entry>
<entry><literal>43 years 8 mons 3 days</literal></entry>
</row>
<row>
<entry><function>age</function>(<type>timestamp</type>, <type>timestamp</type>)</entry>
<entry><type>interval</type></entry>
<entry>Subtract arguments</entry>
<entry><literal>age('2001-04-10', timestamp '1957-06-13')</literal></entry>
<entry><literal>43 years 9 mons 27 days</literal></entry>
</row>
<row>
<entry><function>current_date</function></entry>
<entry><type>date</type></entry>
<entry>Today's date; see <xref linkend="functions-datetime-current">
</entry>
<entry></entry>
<entry></entry>
</row>
<row>
<entry><function>current_time</function></entry>
<entry><type>time with time zone</type></entry>
<entry>Time of day; see <xref linkend="functions-datetime-current">
</entry>
<entry></entry>
<entry></entry>
</row>
<row>
<entry><function>current_timestamp</function></entry>
<entry><type>timestamp with time zone</type></entry>
<entry>Date and time; see <xref linkend="functions-datetime-current">
</entry>
<entry></entry>
<entry></entry>
</row>
<row>
<entry><function>date_part</function>(<type>text</type>, <type>timestamp</type>)</entry>
<entry><type>double precision</type></entry>
<entry>Get subfield (equivalent to
<function>extract</function>); see also <link
linkend="functions-datetime-datepart">below</link>
</entry>
<entry><literal>date_part('hour', timestamp '2001-02-16 20:38:40')</literal></entry>
<entry><literal>20</literal></entry>
</row>
<row>
<entry><function>date_part</function>(<type>text</type>, <type>interval</type>)</entry>
<entry><type>double precision</type></entry>
<entry>Get subfield (equivalent to
<function>extract</function>); see also <link
linkend="functions-datetime-datepart">below</link>
</entry>
<entry><literal>date_part('month', interval '2 years 3 months')</literal></entry>
<entry><literal>3</literal></entry>
</row>
<row>
<entry><function>date_trunc</function>(<type>text</type>, <type>timestamp</type>)</entry>
<entry><type>timestamp</type></entry>
<entry>Truncate to specified precision; see also <xref
linkend="functions-datetime-trunc">
</entry>
<entry><literal>date_trunc('hour', timestamp '2001-02-16 20:38:40')</literal></entry>
<entry><literal>2001-02-16 20:00:00+00</literal></entry>
</row>
<row>
<entry><function>extract</function>(<parameter>field</parameter> from
<type>timestamp</type>)</entry>
<entry><type>double precision</type></entry>
<entry>Get subfield; see also <xref
linkend="functions-datetime-extract">
</entry>
<entry><literal>extract(hour from timestamp '2001-02-16 20:38:40')</literal></entry>
<entry><literal>20</literal></entry>
</row>
<row>
<entry><function>extract</function>(<parameter>field</parameter> from
<type>interval</type>)</entry>
<entry><type>double precision</type></entry>
<entry>Get subfield; see also <xref
linkend="functions-datetime-extract">
</entry>
<entry><literal>extract(month from interval '2 years 3 months')</literal></entry>
<entry><literal>3</literal></entry>
</row>
<row>
<entry><function>isfinite</function>(<type>timestamp</type>)</entry>
<entry><type>boolean</type></entry>
<entry>Test for finite time stamp (neither invalid nor infinity)</entry>
<entry><literal>isfinite(timestamp '2001-02-16 21:28:30')</literal></entry>
<entry><literal>true</literal></entry>
</row>
<row>
<entry><function>isfinite</function>(<type>interval</type>)</entry>
<entry><type>boolean</type></entry>
<entry>Test for finite interval</entry>
<entry><literal>isfinite(interval '4 hours')</literal></entry>
<entry><literal>true</literal></entry>
</row>
<row>
<entry><function>localtime</function></entry>
<entry><type>time</type></entry>
<entry>Time of day; see <xref linkend="functions-datetime-current">
</entry>
<entry></entry>
<entry></entry>
</row>
<row>
<entry><function>localtimestamp</function></entry>
<entry><type>timestamp</type></entry>
<entry>Date and time; see <xref linkend="functions-datetime-current">
</entry>
<entry></entry>
<entry></entry>
</row>
<row>
<entry><function>now</function>()</entry>
<entry><type>timestamp with time zone</type></entry>
<entry>Current date and time (equivalent to
<function>current_timestamp</function>); see <xref
linkend="functions-datetime-current">
</entry>
<entry></entry>
<entry></entry>
</row>
<row>
<entry><function>timeofday()</function></entry>
<entry><type>text</type></entry>
<entry>Current date and time; see <xref
linkend="functions-datetime-current">
</entry>
<entry><literal>timeofday()</literal></entry>
<entry><literal>Wed Feb 21 17:01:13.000126 2001 EST</literal></entry>
</row>
</tbody>
</tgroup>
</table>
<sect2 id="functions-datetime-extract">
<title><function>EXTRACT</function>, <function>date_part</function></title>
<synopsis>
EXTRACT (<replaceable>field</replaceable> FROM <replaceable>source</replaceable>)
</synopsis>
<para>
The <function>extract</function> function retrieves subfields
from date/time values, such as year or hour.
<replaceable>source</replaceable> is a value expression that
evaluates to type <type>timestamp</type> or <type>interval</type>.
(Expressions of type <type>date</type> or <type>time</type> will
be cast to <type>timestamp</type> and can therefore be used as
well.) <replaceable>field</replaceable> is an identifier or
string that selects what field to extract from the source value.
The <function>extract</function> function returns values of type
<type>double precision</type>.
The following are valid values:
<!-- alphabetical -->
<variablelist>
<varlistentry>
<term><literal>century</literal></term>
<listitem>
<para>
The year field divided by 100
</para>
<screen>
SELECT EXTRACT(CENTURY FROM TIMESTAMP '2001-02-16 20:38:40');
<lineannotation>Result: </lineannotation><computeroutput>20</computeroutput>
</screen>
<para>
Note that the result for the century field is simply the year field
divided by 100, and not the conventional definition which puts most
years in the 1900's in the twentieth century.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>day</literal></term>
<listitem>
<para>
The day (of the month) field (1 - 31)
</para>
<screen>
SELECT EXTRACT(DAY FROM TIMESTAMP '2001-02-16 20:38:40');
<lineannotation>Result: </lineannotation><computeroutput>16</computeroutput>
</screen>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>decade</literal></term>
<listitem>
<para>
The year field divided by 10
</para>
<screen>
SELECT EXTRACT(DECADE FROM TIMESTAMP '2001-02-16 20:38:40');
<lineannotation>Result: </lineannotation><computeroutput>200</computeroutput>
</screen>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>dow</literal></term>
<listitem>
<para>
The day of the week (0 - 6; Sunday is 0) (for
<type>timestamp</type> values only)
</para>
<screen>
SELECT EXTRACT(DOW FROM TIMESTAMP '2001-02-16 20:38:40');
<lineannotation>Result: </lineannotation><computeroutput>5</computeroutput>
</screen>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>doy</literal></term>
<listitem>
<para>
The day of the year (1 - 365/366) (for <type>timestamp</type> values only)
</para>
<screen>
SELECT EXTRACT(DOY FROM TIMESTAMP '2001-02-16 20:38:40');
<lineannotation>Result: </lineannotation><computeroutput>47</computeroutput>
</screen>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>epoch</literal></term>
<listitem>
<para>
For <type>date</type> and <type>timestamp</type> values, the
number of seconds since 1970-01-01 00:00:00-00 (can be negative);
for <type>interval</type> values, the total number
of seconds in the interval
</para>
<screen>
SELECT EXTRACT(EPOCH FROM TIMESTAMP '2001-02-16 20:38:40');
<lineannotation>Result: </lineannotation><computeroutput>982352320</computeroutput>
SELECT EXTRACT(EPOCH FROM INTERVAL '5 days 3 hours');
<lineannotation>Result: </lineannotation><computeroutput>442800</computeroutput>
</screen>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>hour</literal></term>
<listitem>
<para>
The hour field (0 - 23)
</para>
<screen>
SELECT EXTRACT(HOUR FROM TIMESTAMP '2001-02-16 20:38:40');
<lineannotation>Result: </lineannotation><computeroutput>20</computeroutput>
</screen>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>microseconds</literal></term>
<listitem>
<para>
The seconds field, including fractional parts, multiplied by 1
000 000. Note that this includes full seconds.
</para>
<screen>
SELECT EXTRACT(MICROSECONDS FROM TIME '17:12:28.5');
<lineannotation>Result: </lineannotation><computeroutput>28500000</computeroutput>
</screen>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>millennium</literal></term>
<listitem>
<para>
The year field divided by 1000
</para>
<screen>
SELECT EXTRACT(MILLENNIUM FROM TIMESTAMP '2001-02-16 20:38:40');
<lineannotation>Result: </lineannotation><computeroutput>2</computeroutput>
</screen>
<para>
Note that the result for the millennium field is simply the year field
divided by 1000, and not the conventional definition which puts
years in the 1900's in the second millennium.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>milliseconds</literal></term>
<listitem>
<para>
The seconds field, including fractional parts, multiplied by
1000. Note that this includes full seconds.
</para>
<screen>
SELECT EXTRACT(MILLISECONDS FROM TIME '17:12:28.5');
<lineannotation>Result: </lineannotation><computeroutput>28500</computeroutput>
</screen>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>minute</literal></term>
<listitem>
<para>
The minutes field (0 - 59)
</para>
<screen>
SELECT EXTRACT(MINUTE FROM TIMESTAMP '2001-02-16 20:38:40');
<lineannotation>Result: </lineannotation><computeroutput>38</computeroutput>
</screen>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>month</literal></term>
<listitem>
<para>
For <type>timestamp</type> values, the number of the month
within the year (1 - 12) ; for <type>interval</type> values
the number of months, modulo 12 (0 - 11)
</para>
<screen>
SELECT EXTRACT(MONTH FROM TIMESTAMP '2001-02-16 20:38:40');
<lineannotation>Result: </lineannotation><computeroutput>2</computeroutput>
SELECT EXTRACT(MONTH FROM INTERVAL '2 years 3 months');
<lineannotation>Result: </lineannotation><computeroutput>3</computeroutput>
SELECT EXTRACT(MONTH FROM INTERVAL '2 years 13 months');
<lineannotation>Result: </lineannotation><computeroutput>1</computeroutput>
</screen>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>quarter</literal></term>
<listitem>
<para>
The quarter of the year (1 - 4) that the day is in (for
<type>timestamp</type> values only)
</para>
<screen>
SELECT EXTRACT(QUARTER FROM TIMESTAMP '2001-02-16 20:38:40');
<lineannotation>Result: </lineannotation><computeroutput>1</computeroutput>
</screen>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>second</literal></term>
<listitem>
<para>
The seconds field, including fractional parts (0 -
59<footnote><simpara>60 if leap seconds are
implemented by the operating system</simpara></footnote>)
</para>
<screen>
SELECT EXTRACT(SECOND FROM TIMESTAMP '2001-02-16 20:38:40');
<lineannotation>Result: </lineannotation><computeroutput>40</computeroutput>
SELECT EXTRACT(SECOND FROM TIME '17:12:28.5');
<lineannotation>Result: </lineannotation><computeroutput>28.5</computeroutput>
</screen>
</listitem>
</varlistentry>
<!--
<varlistentry>
<term><literal>timezone</literal></term>
<listitem>
<para>
The time zone offset. XXX But in what units?
</para>
</listitem>
</varlistentry>
-->
<varlistentry>
<term><literal>timezone_hour</literal></term>
<listitem>
<para>
The hour component of the time zone offset.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>timezone_minute</literal></term>
<listitem>
<para>
The minute component of the time zone offset.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>week</literal></term>
<listitem>
<para>
From a <type>timestamp</type> value, calculate the number of
the week of the year that the day is in. By definition
(<acronym>ISO</acronym> 8601), the first week of a year
contains January 4 of that year. (The <acronym>ISO</acronym>
week starts on Monday.) In other words, the first Thursday of
a year is in week 1 of that year.
</para>
<screen>
SELECT EXTRACT(WEEK FROM TIMESTAMP '2001-02-16 20:38:40');
<lineannotation>Result: </lineannotation><computeroutput>7</computeroutput>
</screen>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>year</literal></term>
<listitem>
<para>
The year field
</para>
<screen>
SELECT EXTRACT(YEAR FROM TIMESTAMP '2001-02-16 20:38:40');
<lineannotation>Result: </lineannotation><computeroutput>2001</computeroutput>
</screen>
</listitem>
</varlistentry>
</variablelist>
</para>
<para>
The <function>extract</function> function is primarily intended
for computational processing. For formatting date/time values for
display, see <xref linkend="functions-formatting">.
</para>
<anchor id="functions-datetime-datepart">
<para>
The <function>date_part</function> function is modeled on the traditional
<productname>Ingres</productname> equivalent to the
<acronym>SQL</acronym>-standard function <function>extract</function>:
<synopsis>
date_part('<replaceable>field</replaceable>', <replaceable>source</replaceable>)
</synopsis>
Note that here the <replaceable>field</replaceable> parameter needs to
be a string value, not a name. The valid field values for
<function>date_part</function> are the same as for
<function>extract</function>.
</para>
<screen>
SELECT date_part('day', TIMESTAMP '2001-02-16 20:38:40');
<lineannotation>Result: </lineannotation><computeroutput>16</computeroutput>
SELECT date_part('hour', INTERVAL '4 hours 3 minutes');
<lineannotation>Result: </lineannotation><computeroutput>4</computeroutput>
</screen>
</sect2>
<sect2 id="functions-datetime-trunc">
<title><function>date_trunc</function></title>
<para>
The function <function>date_trunc</function> is conceptually
similar to the <function>trunc</function> function for numbers.
</para>
<para>
<synopsis>
date_trunc('<replaceable>field</replaceable>', <replaceable>source</replaceable>)
</synopsis>
<replaceable>source</replaceable> is a value expression of type
<type>timestamp</type> (values of type <type>date</type> and
<type>time</type> are cast automatically).
<replaceable>field</replaceable> selects to which precision to
truncate the time stamp value. The return value is of type
<type>timestamp</type> with all fields that are less than the
selected one set to zero (or one, for day and month).
</para>
<para>
Valid values for <replaceable>field</replaceable> are:
<simplelist>
<member>microseconds</member>
<member>milliseconds</member>
<member>second</member>
<member>minute</member>
<member>hour</member>
<member>day</member>
<member>month</member>
<member>year</member>
<member>decade</member>
<member>century</member>
<member>millennium</member>
</simplelist>
</para>
<para>
Examples:
<screen>
SELECT date_trunc('hour', TIMESTAMP '2001-02-16 20:38:40');
<lineannotation>Result: </lineannotation><computeroutput>2001-02-16 20:00:00+00</computeroutput>
SELECT date_trunc('year', TIMESTAMP '2001-02-16 20:38:40');
<lineannotation>Result: </lineannotation><computeroutput>2001-01-01 00:00:00+00</computeroutput>
</screen>
</para>
</sect2>
<sect2 id="functions-datetime-zoneconvert">
<title><function>AT TIME ZONE</function></title>
<indexterm>
<primary>timezone</primary>
<secondary>conversion</secondary>
</indexterm>
<para>
The <function>AT TIME ZONE</function> construct allows conversions
of timestamps to different timezones.
</para>
<table id="functions-datetime-zoneconvert-table">
<title>AT TIME ZONE Variants</title>
<tgroup cols="3">
<thead>
<row>
<entry>Expression</entry>
<entry>Returns</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry>
<type>timestamp without time zone</type>
<literal>AT TIME ZONE</literal>
<replaceable>zone</>
</entry>
<entry><type>timestamp with time zone</type></entry>
<entry>Convert local time in given timezone to UTC</entry>
</row>
<row>
<entry>
<type>timestamp with time zone</type>
<literal>AT TIME ZONE</literal>
<replaceable>zone</>
</entry>
<entry><type>timestamp without time zone</type></entry>
<entry>Convert UTC to local time in given timezone</entry>
</row>
<row>
<entry>
<type>time with time zone</type>
<literal>AT TIME ZONE</literal>
<replaceable>zone</>
</entry>
<entry><type>time with time zone</type></entry>
<entry>Convert local time across timezones</entry>
</row>
</tbody>
</tgroup>
</table>
<para>
In these expressions, the desired time <replaceable>zone</> can be
specified either as a text string (e.g., <literal>'PST'</literal>)
or as an interval (e.g., <literal>INTERVAL '-08:00'</literal>).
</para>
<para>
Examples (supposing that <varname>TimeZone</> is <literal>PST8PDT</>):
<screen>
SELECT TIMESTAMP '2001-02-16 20:38:40' AT TIME ZONE 'MST';
<lineannotation>Result: </lineannotation><computeroutput>2001-02-16 19:38:40-08</computeroutput>
SELECT TIMESTAMP WITH TIME ZONE '2001-02-16 20:38:40-05' AT TIME ZONE 'MST';
<lineannotation>Result: </lineannotation><computeroutput>2001-02-16 18:38:40</computeroutput>
</screen>
The first example takes a zone-less timestamp and interprets it as MST time
(GMT-7) to produce a UTC timestamp, which is then rotated to PST (GMT-8)
for display. The second example takes a timestamp specified in EST
(GMT-5) and converts it to local time in MST (GMT-7).
</para>
<para>
The function <function>timezone</function>(<replaceable>zone</>,
<replaceable>timestamp</>) is equivalent to the SQL-compliant construct
<replaceable>timestamp</> <literal>AT TIME ZONE</literal>
<replaceable>zone</>.
</para>
</sect2>
<sect2 id="functions-datetime-current">
<title>Current Date/Time</title>
<indexterm>
<primary>date</primary>
<secondary>current</secondary>
</indexterm>
<indexterm>
<primary>time</primary>
<secondary>current</secondary>
</indexterm>
<para>
The following functions are available to obtain the current date and/or
time:
<synopsis>
CURRENT_DATE
CURRENT_TIME
CURRENT_TIMESTAMP
CURRENT_TIME ( <replaceable>precision</replaceable> )
CURRENT_TIMESTAMP ( <replaceable>precision</replaceable> )
LOCALTIME
LOCALTIMESTAMP
LOCALTIME ( <replaceable>precision</replaceable> )
LOCALTIMESTAMP ( <replaceable>precision</replaceable> )
</synopsis>
</para>
<para>
<function>CURRENT_TIME</function> and
<function>CURRENT_TIMESTAMP</function> deliver values with time zone;
<function>LOCALTIME</function> and
<function>LOCALTIMESTAMP</function> deliver values without time zone.
</para>
<para>
<function>CURRENT_TIME</function>,
<function>CURRENT_TIMESTAMP</function>,
<function>LOCALTIME</function>, and
<function>LOCALTIMESTAMP</function>
can optionally be given
a precision parameter, which causes the result to be rounded
to that many fractional digits. Without a precision parameter,
the result is given to the full available precision.
</para>
<note>
<para>
Prior to <productname>PostgreSQL</productname> 7.2, the precision
parameters were unimplemented, and the result was always given
in integer seconds.
</para>
</note>
<para>
Some examples:
<screen>
SELECT CURRENT_TIME;
<computeroutput>14:39:53.662522-05</computeroutput>
SELECT CURRENT_DATE;
<computeroutput>2001-12-23</computeroutput>
SELECT CURRENT_TIMESTAMP;
<computeroutput>2001-12-23 14:39:53.662522-05</computeroutput>
SELECT CURRENT_TIMESTAMP(2);
<computeroutput>2001-12-23 14:39:53.66-05</computeroutput>
SELECT LOCALTIMESTAMP;
<computeroutput>2001-12-23 14:39:53.662522</computeroutput>
</screen>
</para>
<para>
The function <function>now()</function> is the traditional
<productname>PostgreSQL</productname> equivalent to
<function>CURRENT_TIMESTAMP</function>.
</para>
<para>
There is also <function>timeofday()</function>, which for historical
reasons returns a text string rather than a <type>timestamp</type> value:
<screen>
SELECT timeofday();
Sat Feb 17 19:07:32.000126 2001 EST
</screen>
</para>
<para>
It is important to realize that
<function>CURRENT_TIMESTAMP</function> and related functions return
the start time of the current transaction; their values do not
change during the transaction. <function>timeofday()</function>
returns the wall clock time and does advance during transactions.
</para>
<note>
<para>
Many other database systems advance these values more
frequently.
</para>
</note>
<para>
All the date/time data types also accept the special literal value
<literal>now</literal> to specify the current date and time. Thus,
the following three all return the same result:
<programlisting>
SELECT CURRENT_TIMESTAMP;
SELECT now();
SELECT TIMESTAMP 'now';
</programlisting>
</para>
<note>
<para>
You do not want to use the third form when specifying a <literal>DEFAULT</>
clause while creating a table. The system will convert <literal>now</literal>
to a <type>timestamp</type> as soon as the constant is parsed, so that when
the default value is needed,
the time of the table creation would be used! The first two
forms will not be evaluated until the default value is used,
because they are function calls. Thus they will give the desired
behavior of defaulting to the time of row insertion.
</para>
</note>
</sect2>
</sect1>
<sect1 id="functions-geometry">
<title>Geometric Functions and Operators</title>
<para>
The geometric types <type>point</type>, <type>box</type>,
<type>lseg</type>, <type>line</type>, <type>path</type>,
<type>polygon</type>, and <type>circle</type> have a large set of
native support functions and operators, shown in <xref
linkend="functions-geometry-op-table">, <xref
linkend="functions-geometry-func-table">, and <xref
linkend="functions-geometry-conv-table">.
</para>
<table id="functions-geometry-op-table">
<title>Geometric Operators</title>
<tgroup cols="3">
<thead>
<row>
<entry>Operator</entry>
<entry>Description</entry>
<entry>Usage</entry>
</row>
</thead>
<tbody>
<row>
<entry> + </entry>
<entry>Translation</entry>
<entry><literal>box '((0,0),(1,1))' + point '(2.0,0)'</literal></entry>
</row>
<row>
<entry> - </entry>
<entry>Translation</entry>
<entry><literal>box '((0,0),(1,1))' - point '(2.0,0)'</literal></entry>
</row>
<row>
<entry> * </entry>
<entry>Scaling/rotation</entry>
<entry><literal>box '((0,0),(1,1))' * point '(2.0,0)'</literal></entry>
</row>
<row>
<entry> / </entry>
<entry>Scaling/rotation</entry>
<entry><literal>box '((0,0),(2,2))' / point '(2.0,0)'</literal></entry>
</row>
<row>
<entry> # </entry>
<entry>Intersection</entry>
<entry><literal>'((1,-1),(-1,1))' # '((1,1),(-1,-1))'</literal></entry>
</row>
<row>
<entry> # </entry>
<entry>Number of points in path or polygon</entry>
<entry><literal># '((1,0),(0,1),(-1,0))'</literal></entry>
</row>
<row>
<entry> @-@ </entry>
<entry>Length or circumference</entry>
<entry><literal>@-@ path '((0,0),(1,0))'</literal></entry>
</row>
<row>
<entry> @@ </entry>
<entry>Center of</entry>
<entry><literal>@@ circle '((0,0),10)'</literal></entry>
</row>
<row>
<entry> ## </entry>
<entry>Point of closest proximity</entry>
<entry><literal>point '(0,0)' ## lseg '((2,0),(0,2))'</literal></entry>
</row>
<row>
<entry> &lt;-&gt; </entry>
<entry>Distance between</entry>
<entry><literal>circle '((0,0),1)' &lt;-&gt; circle '((5,0),1)'</literal></entry>
</row>
<row>
<entry> &amp;&amp; </entry>
<entry>Overlaps?</entry>
<entry><literal>box '((0,0),(1,1))' &amp;&amp; box '((0,0),(2,2))'</literal></entry>
</row>
<row>
<entry> &amp;&lt; </entry>
<entry>Overlaps or is left of?</entry>
<entry><literal>box '((0,0),(1,1))' &amp;&lt; box '((0,0),(2,2))'</literal></entry>
</row>
<row>
<entry> &amp;&gt; </entry>
<entry>Overlaps or is right of?</entry>
<entry><literal>box '((0,0),(3,3))' &amp;&gt; box '((0,0),(2,2))'</literal></entry>
</row>
<row>
<entry> &lt;&lt; </entry>
<entry>Left of?</entry>
<entry><literal>circle '((0,0),1)' &lt;&lt; circle '((5,0),1)'</literal></entry>
</row>
<row>
<entry> &gt;&gt; </entry>
<entry>Right of?</entry>
<entry><literal>circle '((5,0),1)' &gt;&gt; circle '((0,0),1)'</literal></entry>
</row>
<row>
<entry> &lt;^ </entry>
<entry>Below?</entry>
<entry><literal>circle '((0,0),1)' &lt;^ circle '((0,5),1)'</literal></entry>
</row>
<row>
<entry> &gt;^ </entry>
<entry>Above?</entry>
<entry><literal>circle '((0,5),1)' >^ circle '((0,0),1)'</literal></entry>
</row>
<row>
<entry> ?# </entry>
<entry>Intersect?</entry>
<entry><literal>lseg '((-1,0),(1,0))' ?# box '((-2,-2),(2,2))'</literal></entry>
</row>
<row>
<entry> ?- </entry>
<entry>Horizontal?</entry>
<entry><literal>?- lseg '((-1,0),(1,0))'</literal></entry>
</row>
<row>
<entry> ?- </entry>
<entry>Horizontally aligned?</entry>
<entry><literal>point '(1,0)' ?- point '(0,0)'</literal></entry>
</row>
<row>
<entry> ?| </entry>
<entry>Vertical?</entry>
<entry><literal>?| lseg '((-1,0),(1,0))'</literal></entry>
</row>
<row>
<entry> ?| </entry>
<entry>Vertically aligned?</entry>
<entry><literal>point '(0,1)' ?| point '(0,0)'</literal></entry>
</row>
<row>
<entry> ?-| </entry>
<entry>Perpendicular?</entry>
<entry><literal>lseg '((0,0),(0,1))' ?-| lseg '((0,0),(1,0))'</literal></entry>
</row>
<row>
<entry> ?|| </entry>
<entry>Parallel?</entry>
<entry><literal>lseg '((-1,0),(1,0))' ?|| lseg '((-1,2),(1,2))'</literal></entry>
</row>
<row>
<entry> ~ </entry>
<entry>Contains?</entry>
<entry><literal>circle '((0,0),2)' ~ point '(1,1)'</literal></entry>
</row>
<row>
<entry> @ </entry>
<entry>Contained in or on?</entry>
<entry><literal>point '(1,1)' @ circle '((0,0),2)'</literal></entry>
</row>
<row>
<entry> ~= </entry>
<entry>Same as?</entry>
<entry><literal>polygon '((0,0),(1,1))' ~= polygon '((1,1),(0,0))'</literal></entry>
</row>
</tbody>
</tgroup>
</table>
<table id="functions-geometry-func-table">
<title>Geometric Functions</title>
<tgroup cols="4">
<thead>
<row>
<entry>Function</entry>
<entry>Returns</entry>
<entry>Description</entry>
<entry>Example</entry>
</row>
</thead>
<tbody>
<row>
<entry><function>area</function>(object)</entry>
<entry><type>double precision</type></entry>
<entry>area of item</entry>
<entry><literal>area(box '((0,0),(1,1))')</literal></entry>
</row>
<row>
<entry><function>box</function>(box, box)</entry>
<entry><type>box</type></entry>
<entry>intersection box</entry>
<entry><literal>box(box '((0,0),(1,1))',box '((0.5,0.5),(2,2))')</literal></entry>
</row>
<row>
<entry><function>center</function>(object)</entry>
<entry><type>point</type></entry>
<entry>center of item</entry>
<entry><literal>center(box '((0,0),(1,2))')</literal></entry>
</row>
<row>
<entry><function>diameter</function>(circle)</entry>
<entry><type>double precision</type></entry>
<entry>diameter of circle</entry>
<entry><literal>diameter(circle '((0,0),2.0)')</literal></entry>
</row>
<row>
<entry><function>height</function>(box)</entry>
<entry><type>double precision</type></entry>
<entry>vertical size of box</entry>
<entry><literal>height(box '((0,0),(1,1))')</literal></entry>
</row>
<row>
<entry><function>isclosed</function>(path)</entry>
<entry><type>boolean</type></entry>
<entry>a closed path?</entry>
<entry><literal>isclosed(path '((0,0),(1,1),(2,0))')</literal></entry>
</row>
<row>
<entry><function>isopen</function>(path)</entry>
<entry><type>boolean</type></entry>
<entry>an open path?</entry>
<entry><literal>isopen(path '[(0,0),(1,1),(2,0)]')</literal></entry>
</row>
<row>
<entry><function>length</function>(object)</entry>
<entry><type>double precision</type></entry>
<entry>length of item</entry>
<entry><literal>length(path '((-1,0),(1,0))')</literal></entry>
</row>
<row>
<entry><function>npoints</function>(path)</entry>
<entry><type>integer</type></entry>
<entry>number of points</entry>
<entry><literal>npoints(path '[(0,0),(1,1),(2,0)]')</literal></entry>
</row>
<row>
<entry><function>npoints</function>(polygon)</entry>
<entry><type>integer</type></entry>
<entry>number of points</entry>
<entry><literal>npoints(polygon '((1,1),(0,0))')</literal></entry>
</row>
<row>
<entry><function>pclose</function>(path)</entry>
<entry><type>path</type></entry>
<entry>convert path to closed</entry>
<entry><literal>popen(path '[(0,0),(1,1),(2,0)]')</literal></entry>
</row>
<![IGNORE[
<!-- Not defined by this name. Implements the intersection operator '#' -->
<row>
<entry><function>point</function>(lseg,lseg)</entry>
<entry><type>point</type></entry>
<entry>intersection</entry>
<entry><literal>point(lseg '((-1,0),(1,0))',lseg '((-2,-2),(2,2))')</literal></entry>
</row>
]]>
<row>
<entry><function>popen</function>(path)</entry>
<entry><type>path</type></entry>
<entry>convert path to open path</entry>
<entry><literal>popen(path '((0,0),(1,1),(2,0))')</literal></entry>
</row>
<row>
<entry><function>radius</function>(circle)</entry>
<entry><type>double precision</type></entry>
<entry>radius of circle</entry>
<entry><literal>radius(circle '((0,0),2.0)')</literal></entry>
</row>
<row>
<entry><function>width</function>(box)</entry>
<entry><type>double precision</type></entry>
<entry>horizontal size</entry>
<entry><literal>width(box '((0,0),(1,1))')</literal></entry>
</row>
</tbody>
</tgroup>
</table>
<table id="functions-geometry-conv-table">
<title>Geometric Type Conversion Functions</title>
<tgroup cols="4">
<thead>
<row>
<entry>Function</entry>
<entry>Returns</entry>
<entry>Description</entry>
<entry>Example</entry>
</row>
</thead>
<tbody>
<row>
<entry><function>box</function>(<type>circle</type>)</entry>
<entry><type>box</type></entry>
<entry>circle to box</entry>
<entry><literal>box(circle '((0,0),2.0)')</literal></entry>
</row>
<row>
<entry><function>box</function>(<type>point</type>, <type>point</type>)</entry>
<entry><type>box</type></entry>
<entry>points to box</entry>
<entry><literal>box(point '(0,0)', point '(1,1)')</literal></entry>
</row>
<row>
<entry><function>box</function>(<type>polygon</type>)</entry>
<entry><type>box</type></entry>
<entry>polygon to box</entry>
<entry><literal>box(polygon '((0,0),(1,1),(2,0))')</literal></entry>
</row>
<row>
<entry><function>circle</function>(<type>box</type>)</entry>
<entry><type>circle</type></entry>
<entry>to circle</entry>
<entry><literal>circle(box '((0,0),(1,1))')</literal></entry>
</row>
<row>
<entry><function>circle</function>(<type>point</type>, <type>double precision</type>)</entry>
<entry><type>circle</type></entry>
<entry>point to circle</entry>
<entry><literal>circle(point '(0,0)', 2.0)</literal></entry>
</row>
<row>
<entry><function>lseg</function>(<type>box</type>)</entry>
<entry><type>lseg</type></entry>
<entry>box diagonal to <type>lseg</type></entry>
<entry><literal>lseg(box '((-1,0),(1,0))')</literal></entry>
</row>
<row>
<entry><function>lseg</function>(<type>point</type>, <type>point</type>)</entry>
<entry><type>lseg</type></entry>
<entry>points to <type>lseg</type></entry>
<entry><literal>lseg(point '(-1,0)', point '(1,0)')</literal></entry>
</row>
<row>
<entry><function>path</function>(<type>polygon</type>)</entry>
<entry><type>point</type></entry>
<entry>polygon to path</entry>
<entry><literal>path(polygon '((0,0),(1,1),(2,0))')</literal></entry>
</row>
<row>
<entry><function>point</function>(<type>circle</type>)</entry>
<entry><type>point</type></entry>
<entry>center</entry>
<entry><literal>point(circle '((0,0),2.0)')</literal></entry>
</row>
<row>
<entry><function>point</function>(<type>lseg</type>, <type>lseg</type>)</entry>
<entry><type>point</type></entry>
<entry>intersection</entry>
<entry><literal>point(lseg '((-1,0),(1,0))', lseg '((-2,-2),(2,2))')</literal></entry>
</row>
<row>
<entry><function>point</function>(<type>polygon</type>)</entry>
<entry><type>point</type></entry>
<entry>center</entry>
<entry><literal>point(polygon '((0,0),(1,1),(2,0))')</literal></entry>
</row>
<row>
<entry><function>polygon</function>(<type>box</type>)</entry>
<entry><type>polygon</type></entry>
<entry>4-point polygon</entry>
<entry><literal>polygon(box '((0,0),(1,1))')</literal></entry>
</row>
<row>
<entry><function>polygon</function>(<type>circle</type>)</entry>
<entry><type>polygon</type></entry>
<entry>12-point polygon</entry>
<entry><literal>polygon(circle '((0,0),2.0)')</literal></entry>
</row>
<row>
<entry><function>polygon</function>(<replaceable class="parameter">npts</replaceable>, <type>circle</type>)</entry>
<entry><type>polygon</type></entry>
<entry><replaceable class="parameter">npts</replaceable> polygon</entry>
<entry><literal>polygon(12, circle '((0,0),2.0)')</literal></entry>
</row>
<row>
<entry><function>polygon</function>(<type>path</type>)</entry>
<entry><type>polygon</type></entry>
<entry>path to polygon</entry>
<entry><literal>polygon(path '((0,0),(1,1),(2,0))')</literal></entry>
</row>
</tbody>
</tgroup>
</table>
<para>
It is possible to access the two component numbers of a <type>point</>
as though it were an array with subscripts 0, 1. For example, if
<literal>t.p</> is a <type>point</> column then
<literal>SELECT p[0] FROM t</> retrieves the X coordinate;
<literal>UPDATE t SET p[1] = ...</> changes the Y coordinate.
In the same way, a <type>box</> or an <type>lseg</> may be treated
as an array of two <type>point</>s.
</para>
</sect1>
<sect1 id="functions-net">
<title>Network Address Type Functions</title>
<para>
<xref linkend="cidr-inet-operators-table"> shows the operators
available for the <type>inet</type> and <type>cidr</type> types.
The operators <literal>&lt;&lt;</literal>,
<literal>&lt;&lt;=</literal>, <literal>&gt;&gt;</literal>,
<literal>&gt;&gt;=</literal> test for subnet inclusion: they
consider only the network parts of the two addresses, ignoring any
host part, and determine whether one network part is identical to
or a subnet of the other.
</para>
<table tocentry="1" id="cidr-inet-operators-table">
<title><type>cidr</type> and <type>inet</type> Operators</title>
<tgroup cols="3">
<thead>
<row>
<entry>Operator</entry>
<entry>Description</entry>
<entry>Usage</entry>
</row>
</thead>
<tbody>
<row>
<entry> &lt; </entry>
<entry>Less than</entry>
<entry><literal>inet '192.168.1.5' &lt; inet '192.168.1.6'</literal></entry>
</row>
<row>
<entry> &lt;= </entry>
<entry>Less than or equal</entry>
<entry><literal>inet '192.168.1.5' &lt;= inet '192.168.1.5'</literal></entry>
</row>
<row>
<entry> = </entry>
<entry>Equals</entry>
<entry><literal>inet '192.168.1.5' = inet '192.168.1.5'</literal></entry>
</row>
<row>
<entry> &gt;= </entry>
<entry>Greater or equal</entry>
<entry><literal>inet '192.168.1.5' &gt;= inet '192.168.1.5'</literal></entry>
</row>
<row>
<entry> &gt; </entry>
<entry>Greater</entry>
<entry><literal>inet '192.168.1.5' &gt; inet '192.168.1.4'</literal></entry>
</row>
<row>
<entry> &lt;&gt; </entry>
<entry>Not equal</entry>
<entry><literal>inet '192.168.1.5' &lt;&gt; inet '192.168.1.4'</literal></entry>
</row>
<row>
<entry> &lt;&lt; </entry>
<entry>is contained within</entry>
<entry><literal>inet '192.168.1.5' &lt;&lt; inet '192.168.1/24'</literal></entry>
</row>
<row>
<entry> &lt;&lt;= </entry>
<entry>is contained within or equals</entry>
<entry><literal>inet '192.168.1/24' &lt;&lt;= inet '192.168.1/24'</literal></entry>
</row>
<row>
<entry> &gt;&gt; </entry>
<entry>contains</entry>
<entry><literal>inet'192.168.1/24' &gt;&gt; inet '192.168.1.5'</literal></entry>
</row>
<row>
<entry> &gt;&gt;= </entry>
<entry>contains or equals</entry>
<entry><literal>inet '192.168.1/24' &gt;&gt;= inet '192.168.1/24'</literal></entry>
</row>
</tbody>
</tgroup>
</table>
<para>
<xref linkend="cidr-inet-functions-table"> shows the functions
available for use with the <type>inet</type> and <type>cidr</type>
types. The <function>host()</function>,
<function>text()</function>, and <function>abbrev()</function>
functions are primarily intended to offer alternative display
formats. You can cast a text field to inet using normal casting
syntax: <literal>inet(expression)</literal> or
<literal>colname::inet</literal>.
</para>
<table tocentry="1" id="cidr-inet-functions-table">
<title><type>cidr</type> and <type>inet</type> Functions</title>
<tgroup cols="5">
<thead>
<row>
<entry>Function</entry>
<entry>Returns</entry>
<entry>Description</entry>
<entry>Example</entry>
<entry>Result</entry>
</row>
</thead>
<tbody>
<row>
<entry><function>broadcast</function>(<type>inet</type>)</entry>
<entry><type>inet</type></entry>
<entry>broadcast address for network</entry>
<entry><literal>broadcast('192.168.1.5/24')</literal></entry>
<entry><literal>192.168.1.255/24</literal></entry>
</row>
<row>
<entry><function>host</function>(<type>inet</type>)</entry>
<entry><type>text</type></entry>
<entry>extract IP address as text</entry>
<entry><literal>host('192.168.1.5/24')</literal></entry>
<entry><literal>192.168.1.5</literal></entry>
</row>
<row>
<entry><function>masklen</function>(<type>inet</type>)</entry>
<entry><type>integer</type></entry>
<entry>extract netmask length</entry>
<entry><literal>masklen('192.168.1.5/24')</literal></entry>
<entry><literal>24</literal></entry>
</row>
<row>
<entry><function>set_masklen</function>(<type>inet</type>,<type>integer</type>)</entry>
<entry><type>inet</type></entry>
<entry>set netmask length for <type>inet</type> value</entry>
<entry><literal>set_masklen('192.168.1.5/24',16)</literal></entry>
<entry><literal>192.168.1.5/16</literal></entry>
</row>
<row>
<entry><function>netmask</function>(<type>inet</type>)</entry>
<entry><type>inet</type></entry>
<entry>construct netmask for network</entry>
<entry><literal>netmask('192.168.1.5/24')</literal></entry>
<entry><literal>255.255.255.0</literal></entry>
</row>
<row>
<entry><function>network</function>(<type>inet</type>)</entry>
<entry><type>cidr</type></entry>
<entry>extract network part of address</entry>
<entry><literal>network('192.168.1.5/24')</literal></entry>
<entry><literal>192.168.1.0/24</literal></entry>
</row>
<row>
<entry><function>text</function>(<type>inet</type>)</entry>
<entry><type>text</type></entry>
<entry>extract IP address and masklen as text</entry>
<entry><literal>text(inet '192.168.1.5')</literal></entry>
<entry><literal>192.168.1.5/32</literal></entry>
</row>
<row>
<entry><function>abbrev</function>(<type>inet</type>)</entry>
<entry><type>text</type></entry>
<entry>extract abbreviated display as text</entry>
<entry><literal>abbrev(cidr '10.1.0.0/16')</literal></entry>
<entry><literal>10.1/16</literal></entry>
</row>
</tbody>
</tgroup>
</table>
<para>
<xref linkend="macaddr-functions-table"> shows the functions
available for use with the <type>mac</type> type. The function
<function>trunc</function>(<type>macaddr</type>) returns a MAC
address with the last 3 bytes set to 0. This can be used to
associate the remaining prefix with a manufacturer. The directory
<filename>contrib/mac</filename> in the source distribution
contains some utilities to create and maintain such an association
table.
</para>
<table tocentry="1" id="macaddr-functions-table">
<title><type>macaddr</type> Functions</title>
<tgroup cols="5">
<thead>
<row>
<entry>Function</entry>
<entry>Returns</entry>
<entry>Description</entry>
<entry>Example</entry>
<entry>Result</entry>
</row>
</thead>
<tbody>
<row>
<entry><function>trunc</function>(<type>macaddr</type>)</entry>
<entry><type>macaddr</type></entry>
<entry>set last 3 bytes to zero</entry>
<entry><literal>trunc(macaddr '12:34:56:78:90:ab')</literal></entry>
<entry><literal>12:34:56:00:00:00</literal></entry>
</row>
</tbody>
</tgroup>
</table>
<para>
The <type>macaddr</type> type also supports the standard relational
operators (<literal>&gt;</literal>, <literal>&lt;=</literal>, etc.) for
lexicographical ordering.
</para>
</sect1>
<sect1 id="functions-sequence">
<title>Sequence-Manipulation Functions</title>
<indexterm>
<primary>sequences</primary>
</indexterm>
<indexterm>
<primary>nextval</primary>
</indexterm>
<indexterm>
<primary>currval</primary>
</indexterm>
<indexterm>
<primary>setval</primary>
</indexterm>
<para>
This section describes <productname>PostgreSQL</productname>'s functions
for operating on <firstterm>sequence objects</firstterm>.
Sequence objects (also called sequence generators or
just sequences) are special single-row tables created with
<command>CREATE SEQUENCE</command>. A sequence object is usually used to
generate unique identifiers for rows of a table. The sequence functions,
listed in <xref linkend="functions-sequence-table">,
provide simple, multiuser-safe methods for obtaining successive
sequence values from sequence objects.
</para>
<table id="functions-sequence-table">
<title>Sequence Functions</title>
<tgroup cols="3">
<thead>
<row><entry>Function</entry> <entry>Returns</entry> <entry>Description</entry></row>
</thead>
<tbody>
<row>
<entry><function>nextval</function>(<type>text</type>)</entry>
<entry><type>bigint</type></entry>
<entry>Advance sequence and return new value</entry>
</row>
<row>
<entry><function>currval</function>(<type>text</type>)</entry>
<entry><type>bigint</type></entry>
<entry>Return value most recently obtained with <function>nextval</function></entry>
</row>
<row>
<entry><function>setval</function>(<type>text</type>,<type>bigint</type>)</entry>
<entry><type>bigint</type></entry>
<entry>Set sequence's current value</entry>
</row>
<row>
<entry><function>setval</function>(<type>text</type>,<type>bigint</type>,<type>boolean</type>)</entry>
<entry><type>bigint</type></entry>
<entry>Set sequence's current value and <literal>is_called</literal> flag</entry>
</row>
</tbody>
</tgroup>
</table>
<para>
For largely historical reasons, the sequence to be operated on by a
sequence-function call is specified by a text-string argument. To
achieve some compatibility with the handling of ordinary
<acronym>SQL</acronym> names, the sequence functions convert their
argument to lower case unless the string is double-quoted. Thus
<programlisting>
nextval('foo') <lineannotation>operates on sequence <literal>foo</literal></>
nextval('FOO') <lineannotation>operates on sequence <literal>foo</literal></>
nextval('"Foo"') <lineannotation>operates on sequence <literal>Foo</literal></>
</programlisting>
The sequence name can be schema-qualified if necessary:
<programlisting>
nextval('myschema.foo') <lineannotation>operates on <literal>myschema.foo</literal></>
nextval('"myschema".foo') <lineannotation>same as above</lineannotation>
nextval('foo') <lineannotation>searches search path for <literal>foo</literal></>
</programlisting>
Of course, the text argument can be the result of an expression,
not only a simple literal, which is occasionally useful.
</para>
<para>
The available sequence functions are:
<variablelist>
<varlistentry>
<term><function>nextval</function></term>
<listitem>
<para>
Advance the sequence object to its next value and return that
value. This is done atomically: even if multiple sessions
execute <function>nextval</function> concurrently, each will safely receive
a distinct sequence value.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><function>currval</function></term>
<listitem>
<para>
Return the value most recently obtained by <function>nextval</function>
for this sequence in the current session. (An error is
reported if <function>nextval</function> has never been called for this
sequence in this session.) Notice that because this is returning
a session-local value, it gives a predictable answer even if other
sessions are executing <function>nextval</function> meanwhile.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><function>setval</function></term>
<listitem>
<para>
Reset the sequence object's counter value. The two-parameter
form sets the sequence's <literal>last_value</literal> field to the specified
value and sets its <literal>is_called</literal> field to <literal>true</literal>,
meaning that the next <function>nextval</function> will advance the sequence
before returning a value. In the three-parameter form,
<literal>is_called</literal> may be set either <literal>true</literal> or
<literal>false</literal>. If it's set to <literal>false</literal>,
the next <function>nextval</function> will return exactly the specified
value, and sequence advancement commences with the following
<function>nextval</function>. For example,
<screen>
SELECT setval('foo', 42); <lineannotation>Next <function>nextval()</> will return 43</lineannotation>
SELECT setval('foo', 42, true); <lineannotation>Same as above</lineannotation>
SELECT setval('foo', 42, false); <lineannotation>Next <function>nextval()</> will return 42</lineannotation>
</screen>
The result returned by <function>setval</function> is just the value of its
second argument.
</para>
</listitem>
</varlistentry>
</variablelist>
</para>
<important>
<para>
To avoid blocking of concurrent transactions that obtain numbers from the
same sequence, a <function>nextval</function> operation is never rolled back;
that is, once a value has been fetched it is considered used, even if the
transaction that did the <function>nextval</function> later aborts. This means
that aborted transactions may leave unused <quote>holes</quote> in the
sequence of assigned values. <function>setval</function> operations are never
rolled back, either.
</para>
</important>
<para>
If a sequence object has been created with default parameters,
<function>nextval()</function> calls on it will return successive values
beginning with one. Other behaviors can be obtained by using
special parameters in the <command>CREATE SEQUENCE</command> command;
see its command reference page for more information.
</para>
</sect1>
<sect1 id="functions-conditional">
<title>Conditional Expressions</title>
<indexterm>
<primary>case</primary>
</indexterm>
<indexterm>
<primary>conditionals</primary>
</indexterm>
<para>
This section describes the <acronym>SQL</acronym>-compliant conditional expressions
available in <productname>PostgreSQL</productname>.
</para>
<tip>
<para>
If your needs go beyond the capabilities of these conditional
expressions you might want to consider writing a stored procedure
in a more expressive programming language.
</para>
</tip>
<sect2>
<title>CASE</title>
<synopsis>
CASE WHEN <replaceable>condition</replaceable> THEN <replaceable>result</replaceable>
<optional>WHEN ...</optional>
<optional>ELSE <replaceable>result</replaceable></optional>
END
</synopsis>
<para>
The <acronym>SQL</acronym> <token>CASE</token> expression is a
generic conditional expression, similar to if/else statements in
other languages. <token>CASE</token> clauses can be used wherever
an expression is valid. <replaceable>condition</replaceable> is an
expression that returns a <type>boolean</type> result. If the result is true
then the value of the <token>CASE</token> expression is
<replaceable>result</replaceable>. If the result is false any
subsequent <token>WHEN</token> clauses are searched in the same
manner. If no <token>WHEN</token>
<replaceable>condition</replaceable> is true then the value of the
case expression is the <replaceable>result</replaceable> in the
<token>ELSE</token> clause. If the <token>ELSE</token> clause is
omitted and no condition matches, the result is null.
</para>
<para>
An example:
<screen>
<prompt>=&gt;</prompt> <userinput>SELECT * FROM test;</userinput>
<computeroutput>
a
---
1
2
3
</computeroutput>
<prompt>=&gt;</prompt> <userinput>SELECT a,
CASE WHEN a=1 THEN 'one'
WHEN a=2 THEN 'two'
ELSE 'other'
END
FROM test;</userinput>
<computeroutput>
a | case
---+-------
1 | one
2 | two
3 | other
</computeroutput>
</screen>
</para>
<para>
The data types of all the <replaceable>result</replaceable>
expressions must be coercible to a single output type.
See <xref linkend="typeconv-union-case"> for more detail.
</para>
<synopsis>
CASE <replaceable>expression</replaceable>
WHEN <replaceable>value</replaceable> THEN <replaceable>result</replaceable>
<optional>WHEN ...</optional>
<optional>ELSE <replaceable>result</replaceable></optional>
END
</synopsis>
<para>
This <quote>simple</quote> <token>CASE</token> expression is a
specialized variant of the general form above. The
<replaceable>expression</replaceable> is computed and compared to
all the <replaceable>value</replaceable>s in the
<token>WHEN</token> clauses until one is found that is equal. If
no match is found, the <replaceable>result</replaceable> in the
<token>ELSE</token> clause (or a null value) is returned. This is similar
to the <function>switch</function> statement in C.
</para>
<para>
The example above can be written using the simple
<token>CASE</token> syntax:
<screen>
<prompt>=&gt;</prompt> <userinput>SELECT a,
CASE a WHEN 1 THEN 'one'
WHEN 2 THEN 'two'
ELSE 'other'
END
FROM test;</userinput>
<computeroutput>
a | case
---+-------
1 | one
2 | two
3 | other
</computeroutput>
</screen>
</para>
</sect2>
<sect2>
<title>COALESCE</title>
<synopsis>
<function>COALESCE</function>(<replaceable>value</replaceable> <optional>, ...</optional>)
</synopsis>
<para>
The <function>COALESCE</function> function returns the first of its
arguments that is not null. This is often useful to substitute a
default value for null values when data is retrieved for display,
for example:
<programlisting>
SELECT COALESCE(description, short_description, '(none)') ...
</programlisting>
</para>
</sect2>
<sect2>
<title>NULLIF</title>
<indexterm>
<primary>nullif</primary>
</indexterm>
<synopsis>
<function>NULLIF</function>(<replaceable>value1</replaceable>, <replaceable>value2</replaceable>)
</synopsis>
<para>
The <function>NULLIF</function> function returns a null value if and only
if <replaceable>value1</replaceable> and
<replaceable>value2</replaceable> are equal. Otherwise it returns
<replaceable>value1</replaceable>. This can be used to perform the
inverse operation of the <function>COALESCE</function> example
given above:
<programlisting>
SELECT NULLIF(value, '(none)') ...
</programlisting>
</para>
</sect2>
</sect1>
<sect1 id="functions-misc">
<title>Miscellaneous Functions</title>
<para>
<xref linkend="functions-misc-session-table"> shows several
functions that extract session and system information.
</para>
<table id="functions-misc-session-table">
<title>Session Information Functions</title>
<tgroup cols="3">
<thead>
<row><entry>Name</entry> <entry>Return Type</entry> <entry>Description</entry></row>
</thead>
<tbody>
<row>
<entry><function>current_database()</function></entry>
<entry><type>name</type></entry>
<entry>name of current database</entry>
</row>
<row>
<entry><function>current_schema()</function></entry>
<entry><type>name</type></entry>
<entry>name of current schema</entry>
</row>
<row>
<entry><function>current_schemas(boolean)</function></entry>
<entry><type>name[]</type></entry>
<entry>names of schemas in search path optionally including implicit schemas</entry>
</row>
<row>
<entry><function>current_user</function></entry>
<entry><type>name</type></entry>
<entry>user name of current execution context</entry>
</row>
<row>
<entry><function>session_user</function></entry>
<entry><type>name</type></entry>
<entry>session user name</entry>
</row>
<row>
<entry><function>user</function></entry>
<entry><type>name</type></entry>
<entry>equivalent to <function>current_user</function></entry>
</row>
<row>
<entry><function>version()</function></entry>
<entry><type>text</type></entry>
<entry>PostgreSQL version information</entry>
</row>
</tbody>
</tgroup>
</table>
<indexterm zone="functions-misc">
<primary>user</primary>
<secondary>current</secondary>
</indexterm>
<indexterm zone="functions-misc">
<primary>schema</primary>
<secondary>current</secondary>
</indexterm>
<indexterm zone="functions-misc">
<primary>search path</primary>
<secondary>current</secondary>
</indexterm>
<para>
The <function>session_user</function> is the user that initiated a
database connection; it is fixed for the duration of that
connection. The <function>current_user</function> is the user identifier
that is applicable for permission checking. Normally, it is equal
to the session user, but it changes during the execution of
functions with the attribute <literal>SECURITY DEFINER</literal>.
In Unix parlance, the session user is the <quote>real user</quote> and
the current user is the <quote>effective user</quote>.
</para>
<note>
<para>
<function>current_user</function>, <function>session_user</function>, and
<function>user</function> have special syntactic status in <acronym>SQL</acronym>:
they must be called without trailing parentheses.
</para>
</note>
<para>
<function>current_schema</function> returns the name of the schema that is
at the front of the search path (or a null value if the search path is
empty). This is the schema that will be used for any tables or
other named objects that are created without specifying a target schema.
<function>current_schemas(boolean)</function> returns an array of the names of all
schemas presently in the search path. The boolean option determines whether or not
implicitly included system schemas such as pg_catalog are included in the search
path returned.
</para>
<para>
<indexterm>
<primary>search path</primary>
<secondary>changing at runtime</secondary>
</indexterm>
The search path may be altered by a run-time setting. The
command to use is <command>
SET SEARCH_PATH '<varname>schema</varname>'[,'<varname>schema</varname>']...
</command>
</para>
<indexterm zone="functions-misc">
<primary>version</primary>
</indexterm>
<para>
<function>version()</function> returns a string describing the
<productname>PostgreSQL</productname> server's version.
</para>
<para>
<xref linkend="functions-misc-set-table"> shows the functions
available to query and alter run-time configuration parameters.
</para>
<table id="functions-misc-set-table">
<title>Configuration Settings Information Functions</title>
<tgroup cols="3">
<thead>
<row><entry>Name</entry> <entry>Return Type</entry> <entry>Description</entry></row>
</thead>
<tbody>
<row>
<entry>
<function>current_setting</function>(<parameter>setting_name</parameter>)
</entry>
<entry><type>text</type></entry>
<entry>value of current setting</entry>
</row>
<row>
<entry>
<function>set_config(<parameter>setting_name</parameter>,
<parameter>new_value</parameter>,
<parameter>is_local</parameter>)</function>
</entry>
<entry><type>text</type></entry>
<entry>new value of current setting</entry>
</row>
</tbody>
</tgroup>
</table>
<indexterm zone="functions-misc">
<primary>setting</primary>
<secondary>current</secondary>
</indexterm>
<indexterm zone="functions-misc">
<primary>setting</primary>
<secondary>set</secondary>
</indexterm>
<para>
The <function>current_setting</function> is used to obtain the current
value of the <parameter>setting_name</parameter> setting, as a query
result. It is the equivalent to the <acronym>SQL</acronym>
<command>SHOW</command> command.
For example:
<programlisting>
select current_setting('DateStyle');
current_setting
---------------------------------------
ISO with US (NonEuropean) conventions
(1 row)
</programlisting>
</para>
<para>
<function>set_config</function> allows the <parameter>setting_name
</parameter> setting to be changed to <parameter>new_value</parameter>.
If <parameter>is_local</parameter> is set to <literal>true</literal>,
the new value will only apply to the current transaction. If you want
the new value to apply for the current session, use
<literal>false</literal> instead. It is the equivalent to the
<acronym>SQL</acronym> <command>SET</command> command. For example:
<programlisting>
select set_config('show_statement_stats','off','f');
set_config
------------
off
(1 row)
</programlisting>
</para>
<para>
<xref linkend="functions-misc-access-table"> lists functions that
allow the user to query object access privileges programmatically.
See <xref linkend="ddl-priv"> for more information about
privileges.
</para>
<table id="functions-misc-access-table">
<title>Access Privilege Inquiry Functions</title>
<tgroup cols="3">
<thead>
<row><entry>Name</entry> <entry>Return Type</entry> <entry>Description</entry></row>
</thead>
<tbody>
<row>
<entry><function>has_table_privilege</function>(<parameter>user</parameter>,
<parameter>table</parameter>,
<parameter>access</parameter>)
</entry>
<entry><type>boolean</type></entry>
<entry>does user have access to table</entry>
</row>
<row>
<entry><function>has_table_privilege</function>(<parameter>table</parameter>,
<parameter>access</parameter>)
</entry>
<entry><type>boolean</type></entry>
<entry>does current user have access to table</entry>
</row>
<row>
<entry><function>has_database_privilege</function>(<parameter>user</parameter>,
<parameter>database</parameter>,
<parameter>access</parameter>)
</entry>
<entry><type>boolean</type></entry>
<entry>does user have access to database</entry>
</row>
<row>
<entry><function>has_database_privilege</function>(<parameter>database</parameter>,
<parameter>access</parameter>)
</entry>
<entry><type>boolean</type></entry>
<entry>does current user have access to database</entry>
</row>
<row>
<entry><function>has_function_privilege</function>(<parameter>user</parameter>,
<parameter>function</parameter>,
<parameter>access</parameter>)
</entry>
<entry><type>boolean</type></entry>
<entry>does user have access to function</entry>
</row>
<row>
<entry><function>has_function_privilege</function>(<parameter>function</parameter>,
<parameter>access</parameter>)
</entry>
<entry><type>boolean</type></entry>
<entry>does current user have access to function</entry>
</row>
<row>
<entry><function>has_language_privilege</function>(<parameter>user</parameter>,
<parameter>language</parameter>,
<parameter>access</parameter>)
</entry>
<entry><type>boolean</type></entry>
<entry>does user have access to language</entry>
</row>
<row>
<entry><function>has_language_privilege</function>(<parameter>language</parameter>,
<parameter>access</parameter>)
</entry>
<entry><type>boolean</type></entry>
<entry>does current user have access to language</entry>
</row>
<row>
<entry><function>has_schema_privilege</function>(<parameter>user</parameter>,
<parameter>schema</parameter>,
<parameter>access</parameter>)
</entry>
<entry><type>boolean</type></entry>
<entry>does user have access to schema</entry>
</row>
<row>
<entry><function>has_schema_privilege</function>(<parameter>schema</parameter>,
<parameter>access</parameter>)
</entry>
<entry><type>boolean</type></entry>
<entry>does current user have access to schema</entry>
</row>
</tbody>
</tgroup>
</table>
<indexterm zone="functions-misc">
<primary>has_table_privilege</primary>
</indexterm>
<indexterm zone="functions-misc">
<primary>has_database_privilege</primary>
</indexterm>
<indexterm zone="functions-misc">
<primary>has_function_privilege</primary>
</indexterm>
<indexterm zone="functions-misc">
<primary>has_language_privilege</primary>
</indexterm>
<indexterm zone="functions-misc">
<primary>has_schema_privilege</primary>
</indexterm>
<para>
<function>has_table_privilege</function> checks whether a user
can access a table in a particular way. The user can be
specified by name or by ID
(<classname>pg_user</classname>.<structfield>usesysid</structfield>), or if the argument is
omitted
<function>current_user</function> is assumed. The table can be specified
by name or by OID. (Thus, there are actually six variants of
<function>has_table_privilege</function>, which can be distinguished by
the number and types of their arguments.) When specifying by name,
the name can be schema-qualified if necessary.
The desired access type
is specified by a text string, which must evaluate to one of the
values <literal>SELECT</literal>, <literal>INSERT</literal>, <literal>UPDATE</literal>,
<literal>DELETE</literal>, <literal>RULE</literal>, <literal>REFERENCES</literal>, or
<literal>TRIGGER</literal>. (Case of the string is not significant, however.)
An example is:
<programlisting>
SELECT has_table_privilege('myschema.mytable', 'select');
</programlisting>
</para>
<para>
<function>has_database_privilege</function> checks whether a user
can access a database in a particular way. The possibilities for its
arguments are analogous to <function>has_table_privilege</function>.
The desired access type must evaluate to
<literal>CREATE</literal>,
<literal>TEMPORARY</literal>, or
<literal>TEMP</literal> (which is equivalent to
<literal>TEMPORARY</literal>).
</para>
<para>
<function>has_function_privilege</function> checks whether a user
can access a function in a particular way. The possibilities for its
arguments are analogous to <function>has_table_privilege</function>.
When specifying a function by a text string rather than by OID,
the allowed input is the same as for the <type>regprocedure</> data type.
The desired access type must currently evaluate to
<literal>EXECUTE</literal>.
</para>
<para>
<function>has_language_privilege</function> checks whether a user
can access a procedural language in a particular way. The possibilities
for its arguments are analogous to <function>has_table_privilege</function>.
The desired access type must currently evaluate to
<literal>USAGE</literal>.
</para>
<para>
<function>has_schema_privilege</function> checks whether a user
can access a schema in a particular way. The possibilities for its
arguments are analogous to <function>has_table_privilege</function>.
The desired access type must evaluate to
<literal>CREATE</literal> or
<literal>USAGE</literal>.
</para>
<para>
To evaluate whether a user holds a grant option on the privilege,
append <literal> WITH GRANT OPTION</literal> to the privilege key
word; for example <literal>'UPDATE WITH GRANT OPTION'</literal>.
</para>
<para>
<xref linkend="functions-misc-schema-table"> shows functions that
determine whether a certain object is <firstterm>visible</> in the
current schema search path. A table is said to be visible if its
containing schema is in the search path and no table of the same
name appears earlier in the search path. This is equivalent to the
statement that the table can be referenced by name without explicit
schema qualification. For example, to list the names of all
visible tables:
<programlisting>
SELECT relname FROM pg_class WHERE pg_table_is_visible(oid);
</programlisting>
</para>
<table id="functions-misc-schema-table">
<title>Schema Visibility Inquiry Functions</title>
<tgroup cols="3">
<thead>
<row><entry>Name</entry> <entry>Return Type</entry> <entry>Description</entry></row>
</thead>
<tbody>
<row>
<entry><function>pg_table_is_visible</function>(<parameter>tableOID</parameter>)
</entry>
<entry><type>boolean</type></entry>
<entry>is table visible in search path</entry>
</row>
<row>
<entry><function>pg_type_is_visible</function>(<parameter>typeOID</parameter>)
</entry>
<entry><type>boolean</type></entry>
<entry>is type visible in search path</entry>
</row>
<row>
<entry><function>pg_function_is_visible</function>(<parameter>functionOID</parameter>)
</entry>
<entry><type>boolean</type></entry>
<entry>is function visible in search path</entry>
</row>
<row>
<entry><function>pg_operator_is_visible</function>(<parameter>operatorOID</parameter>)
</entry>
<entry><type>boolean</type></entry>
<entry>is operator visible in search path</entry>
</row>
<row>
<entry><function>pg_opclass_is_visible</function>(<parameter>opclassOID</parameter>)
</entry>
<entry><type>boolean</type></entry>
<entry>is operator class visible in search path</entry>
</row>
</tbody>
</tgroup>
</table>
<indexterm zone="functions-misc">
<primary>pg_table_is_visible</primary>
</indexterm>
<indexterm zone="functions-misc">
<primary>pg_type_is_visible</primary>
</indexterm>
<indexterm zone="functions-misc">
<primary>pg_function_is_visible</primary>
</indexterm>
<indexterm zone="functions-misc">
<primary>pg_operator_is_visible</primary>
</indexterm>
<indexterm zone="functions-misc">
<primary>pg_opclass_is_visible</primary>
</indexterm>
<para>
<function>pg_table_is_visible</function> performs the check for
tables (or views, or any other kind of <literal>pg_class</> entry).
<function>pg_type_is_visible</function>,
<function>pg_function_is_visible</function>,
<function>pg_operator_is_visible</function>, and
<function>pg_opclass_is_visible</function> perform the same sort of
visibility check for types, functions, operators, and operator
classes, respectively. For functions and operators, an object in
the search path is visible if there is no object of the same name
<emphasis>and argument data type(s)</> earlier in the path. For
operator classes, both name and associated index access method are
considered.
</para>
<para>
All these functions require object OIDs to identify the object to be
checked. If you want to test an object by name, it is convenient to use
the OID alias types (<type>regclass</>, <type>regtype</>,
<type>regprocedure</>, or <type>regoperator</>), for example
<programlisting>
SELECT pg_type_is_visible('myschema.widget'::regtype);
</programlisting>
Note that it would not make much sense to test an unqualified name in
this way --- if the name can be recognized at all, it must be visible.
</para>
<indexterm zone="functions-misc">
<primary>pg_get_viewdef</primary>
</indexterm>
<indexterm zone="functions-misc">
<primary>pg_get_ruledef</primary>
</indexterm>
<indexterm zone="functions-misc">
<primary>pg_get_indexdef</primary>
</indexterm>
<indexterm zone="functions-misc">
<primary>pg_get_constraintdef</primary>
</indexterm>
<indexterm zone="functions-misc">
<primary>pg_get_userbyid</primary>
</indexterm>
<para>
<xref linkend="functions-misc-catalog-table"> lists functions that
extract information from the system catalogs.
<function>pg_get_viewdef()</function>,
<function>pg_get_ruledef()</function>,
<function>pg_get_indexdef()</function>, and
<function>pg_get_constraintdef()</function> respectively
reconstruct the creating command for a view, rule, index, or
constraint. (Note that this is a decompiled reconstruction, not
the verbatim text of the command.) At present
<function>pg_get_constraintdef()</function> only works for
foreign-key constraints. <function>pg_get_userbyid()</function>
extracts a user's name given a <structfield>usesysid</structfield>
value.
</para>
<table id="functions-misc-catalog-table">
<title>Catalog Information Functions</title>
<tgroup cols="3">
<thead>
<row><entry>Name</entry> <entry>Return Type</entry> <entry>Description</entry></row>
</thead>
<tbody>
<row>
<entry><function>pg_get_viewdef</function>(<parameter>viewname</parameter>)</entry>
<entry><type>text</type></entry>
<entry>Get <command>CREATE VIEW</> command for view (<emphasis>deprecated</emphasis>)</entry>
</row>
<row>
<entry><function>pg_get_viewdef</function>(<parameter>viewOID</parameter>)</entry>
<entry><type>text</type></entry>
<entry>Get <command>CREATE VIEW</> command for view</entry>
</row>
<row>
<entry><function>pg_get_ruledef</function>(<parameter>ruleOID</parameter>)</entry>
<entry><type>text</type></entry>
<entry>Get <command>CREATE RULE</> command for rule</entry>
</row>
<row>
<entry><function>pg_get_indexdef</function>(<parameter>indexOID</parameter>)</entry>
<entry><type>text</type></entry>
<entry>Get <command>CREATE INDEX</> command for index</entry>
</row>
<row>
<entry><function>pg_get_constraintdef</function>(<parameter>constraintOID</parameter>)</entry>
<entry><type>text</type></entry>
<entry>Get definition of a constraint</entry>
</row>
<row>
<entry><function>pg_get_userbyid</function>(<parameter>userid</parameter>)</entry>
<entry><type>name</type></entry>
<entry>Get user name with given ID</entry>
</row>
</tbody>
</tgroup>
</table>
<indexterm zone="functions-misc">
<primary>obj_description</primary>
</indexterm>
<indexterm zone="functions-misc">
<primary>col_description</primary>
</indexterm>
<para>
The function shown in <xref
linkend="functions-misc-comment-table"> extract comments
previously stored with the <command>COMMENT</command> command. A
null value is returned if no comment can be found matching the
specified parameters.
</para>
<table id="functions-misc-comment-table">
<title>Comment Information Functions</title>
<tgroup cols="3">
<thead>
<row><entry>Name</entry> <entry>Return Type</entry> <entry>Description</entry></row>
</thead>
<tbody>
<row>
<entry><function>obj_description</function>(<parameter>objectOID</parameter>, <parameter>tablename</parameter>)</entry>
<entry><type>text</type></entry>
<entry>Get comment for a database object</entry>
</row>
<row>
<entry><function>obj_description</function>(<parameter>objectOID</parameter>)</entry>
<entry><type>text</type></entry>
<entry>Get comment for a database object (<emphasis>deprecated</emphasis>)</entry>
</row>
<row>
<entry><function>col_description</function>(<parameter>tableOID</parameter>, <parameter>columnnumber</parameter>)</entry>
<entry><type>text</type></entry>
<entry>Get comment for a table column</entry>
</row>
</tbody>
</tgroup>
</table>
<para>
The two-parameter form of <function>obj_description()</function> returns the
comment for a database object specified by its OID and the name of the
containing system catalog. For example,
<literal>obj_description(123456,'pg_class')</literal>
would retrieve the comment for a table with OID 123456.
The one-parameter form of <function>obj_description()</function> requires only
the object OID. It is now deprecated since there is no guarantee that
OIDs are unique across different system catalogs; therefore, the wrong
comment could be returned.
</para>
<para>
<function>col_description()</function> returns the comment for a table column,
which is specified by the OID of its table and its column number.
<function>obj_description()</function> cannot be used for table columns since
columns do not have OIDs of their own.
</para>
</sect1>
<sect1 id="functions-aggregate">
<title>Aggregate Functions</title>
<para>
<firstterm>Aggregate functions</firstterm> compute a single result
value from a set of input values. <xref
linkend="functions-aggregate-table"> show the built-in aggregate
functions. The special syntax considerations for aggregate
functions are explained in <xref linkend="syntax-aggregates">.
Consult the &cite-tutorial; for additional introductory
information.
</para>
<table id="functions-aggregate-table">
<title>Aggregate Functions</title>
<tgroup cols="5">
<thead>
<row>
<entry>Function</entry>
<entry>Argument Type</entry>
<entry>Return Type</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry>
<indexterm>
<primary>average</primary>
<secondary>function</secondary>
</indexterm>
<function>avg(<replaceable class="parameter">expression</replaceable>)</function>
</entry>
<entry>
<type>smallint</type>, <type>integer</type>,
<type>bigint</type>, <type>real</type>, <type>double
precision</type>, <type>numeric</type>, or <type>interval</type>.
</entry>
<entry>
<type>numeric</type> for any integer type argument,
<type>double precision</type> for a floating-point argument,
otherwise the same as the argument data type
</entry>
<entry>the average (arithmetic mean) of all input values</entry>
</row>
<row>
<entry><function>count(*)</function></entry>
<entry></entry>
<entry><type>bigint</type></entry>
<entry>number of input values</entry>
</row>
<row>
<entry><function>count(<replaceable class="parameter">expression</replaceable>)</function></entry>
<entry>any</entry>
<entry><type>bigint</type></entry>
<entry>
number of input values for which the value of <replaceable
class="parameter">expression</replaceable> is not null
</entry>
</row>
<row>
<entry><function>max(<replaceable class="parameter">expression</replaceable>)</function></entry>
<entry>any numeric, string, or date/time type</entry>
<entry>same as argument type</entry>
<entry>
maximum value of <replaceable
class="parameter">expression</replaceable> across all input
values
</entry>
</row>
<row>
<entry><function>min(<replaceable class="parameter">expression</replaceable>)</function></entry>
<entry>any numeric, string, or date/time type</entry>
<entry>same as argument type</entry>
<entry>
minimum value of <replaceable
class="parameter">expression</replaceable> across all input
values
</entry>
</row>
<row>
<entry>
<indexterm>
<primary>standard deviation</primary>
</indexterm>
<function>stddev(<replaceable class="parameter">expression</replaceable>)</function>
</entry>
<entry>
<type>smallint</type>, <type>integer</type>,
<type>bigint</type>, <type>real</type>, <type>double
precision</type>, or <type>numeric</type>.
</entry>
<entry>
<type>double precision</type> for floating-point arguments,
otherwise <type>numeric</type>.
</entry>
<entry>sample standard deviation of the input values</entry>
</row>
<row>
<entry><function>sum(<replaceable class="parameter">expression</replaceable>)</function></entry>
<entry>
<type>smallint</type>, <type>integer</type>,
<type>bigint</type>, <type>real</type>, <type>double
precision</type>, <type>numeric</type>, or
<type>interval</type>
</entry>
<entry>
<type>bigint</type> for <type>smallint</type> or
<type>integer</type> arguments, <type>numeric</type> for
<type>bigint</type> arguments, <type>double precision</type>
for floating-point arguments, otherwise the same as the
argument data type
</entry>
<entry>sum of <replaceable class="parameter">expression</replaceable> across all input values</entry>
</row>
<row>
<entry>
<indexterm>
<primary>variance</primary>
</indexterm>
<function>variance</function>(<replaceable class="parameter">expression</replaceable>)
</entry>
<entry>
<type>smallint</type>, <type>integer</type>,
<type>bigint</type>, <type>real</type>, <type>double
precision</type>, or <type>numeric</type>.
</entry>
<entry>
<type>double precision</type> for floating-point arguments,
otherwise <type>numeric</type>.
</entry>
<entry>sample variance of the input values (square of the sample standard deviation)</entry>
</row>
</tbody>
</tgroup>
</table>
<para>
It should be noted that except for <function>count</function>,
these functions return a null value when no rows are selected. In
particular, <function>sum</function> of no rows returns null, not
zero as one might expect. The function <function>coalesce</function> may be
used to substitute zero for null when necessary.
</para>
<note>
<para>
Users accustomed to working with other RDBMS products may be
surprised by the performance characteristics of certain aggregate
functions in <productname>PostgreSQL</productname> when the
aggregate is applied to the entire table (in other words, no
<literal>WHERE</literal> clause is specified). In particular,
a query like
<programlisting>
SELECT min(col) FROM sometable;
</programlisting>
will be executed by <productname>PostgreSQL</productname> using a
sequential scan of the entire table. Other database systems may
optimize queries of this form to use an index on the column, if one
is available. Similarly, the aggregate functions
<function>max()</function> and <function>count()</function> always
require a sequential scan if applied to the entire table in
<productname>PostgreSQL</productname>.
</para>
<para>
<productname>PostgreSQL</productname> cannot easily implement this
optimization because it also allows for user-defined aggregate
queries. Since <function>min()</function>,
<function>max()</function>, and <function>count()</function> are
defined using a generic API for aggregate functions, there is no
provision for <quote>special-casing</quote> the execution of these
functions under certain circumstances.
</para>
<para>
Fortunately, there is a simple workaround for
<function>min()</function> and <function>max()</function>. The
query shown below is equivalent to the query above, except that it
can take advantage of a B+-Tree index if there is one present on
the column in question.
<programlisting>
SELECT col FROM sometable ORDER BY col ASC LIMIT 1;
</programlisting>
A similar query (obtained by substituting <literal>DESC</literal>
for <literal>ASC</literal> in the query above) can be used in the
place of <function>max()</function>).
</para>
<para>
Unfortunately, there is no similarly trivial query that can be
used to improve the performance of <function>count()</function>
when applied to the entire table.
</para>
</note>
</sect1>
<sect1 id="functions-subquery">
<title>Subquery Expressions</title>
<indexterm>
<primary>exists</primary>
</indexterm>
<indexterm>
<primary>in</primary>
</indexterm>
<indexterm>
<primary>not in</primary>
</indexterm>
<indexterm>
<primary>any</primary>
</indexterm>
<indexterm>
<primary>all</primary>
</indexterm>
<indexterm>
<primary>some</primary>
</indexterm>
<indexterm>
<primary>subqueries</primary>
</indexterm>
<para>
This section describes the <acronym>SQL</acronym>-compliant subquery
expressions available in <productname>PostgreSQL</productname>.
All of the expression forms documented in this section return
Boolean (true/false) results.
</para>
<sect2>
<title>EXISTS</title>
<synopsis>
EXISTS ( <replaceable>subquery</replaceable> )
</synopsis>
<para>
The argument of <token>EXISTS</token> is an arbitrary <command>SELECT</> statement,
or <firstterm>subquery</firstterm>. The
subquery is evaluated to determine whether it returns any rows.
If it returns at least one row, the result of <token>EXISTS</token> is
<quote>true</>; if the subquery returns no rows, the result of <token>EXISTS</token>
is <quote>false</>.
</para>
<para>
The subquery can refer to variables from the surrounding query,
which will act as constants during any one evaluation of the subquery.
</para>
<para>
The subquery will generally only be executed far enough to determine
whether at least one row is returned, not all the way to completion.
It is unwise to write a subquery that has any side effects (such as
calling sequence functions); whether the side effects occur or not
may be difficult to predict.
</para>
<para>
Since the result depends only on whether any rows are returned,
and not on the contents of those rows, the output list of the
subquery is normally uninteresting. A common coding convention is
to write all <literal>EXISTS</> tests in the form
<literal>EXISTS(SELECT 1 WHERE ...)</literal>. There are exceptions to
this rule however, such as subqueries that use <token>INTERSECT</token>.
</para>
<para>
This simple example is like an inner join on <literal>col2</>, but
it produces at most one output row for each <literal>tab1</> row,
even if there are multiple matching <literal>tab2</> rows:
<screen>
SELECT col1 FROM tab1
WHERE EXISTS(SELECT 1 FROM tab2 WHERE col2 = tab1.col2);
</screen>
</para>
</sect2>
<sect2>
<title>IN (scalar form)</title>
<synopsis>
<replaceable>expression</replaceable> IN (<replaceable>value</replaceable><optional>, ...</optional>)
</synopsis>
<para>
The right-hand side of this form of <token>IN</token> is a parenthesized list
of scalar expressions. The result is <quote>true</> if the left-hand expression's
result is equal to any of the right-hand expressions. This is a shorthand
notation for
<synopsis>
<replaceable>expression</replaceable> = <replaceable>value1</replaceable>
OR
<replaceable>expression</replaceable> = <replaceable>value2</replaceable>
OR
...
</synopsis>
Note that if the left-hand expression yields null, or if there are
no equal right-hand values and at least one right-hand expression yields
null, the result of the <token>IN</token> construct will be null, not false.
This is in accordance with SQL's normal rules for Boolean combinations
of null values.
</para>
<note>
<para>
This form of <token>IN</token> is not truly a subquery expression, but it
seems best to document it in the same place as subquery <token>IN</token>.
</para>
</note>
</sect2>
<sect2>
<title>IN (subquery form)</title>
<synopsis>
<replaceable>expression</replaceable> IN (<replaceable>subquery</replaceable>)
</synopsis>
<para>
The right-hand side of this form of <token>IN</token> is a parenthesized
subquery, which must return exactly one column. The left-hand expression
is evaluated and compared to each row of the subquery result.
The result of <token>IN</token> is <quote>true</> if any equal subquery row is found.
The result is <quote>false</> if no equal row is found (including the special
case where the subquery returns no rows).
</para>
<para>
Note that if the left-hand expression yields null, or if there are
no equal right-hand values and at least one right-hand row yields
null, the result of the <token>IN</token> construct will be null, not false.
This is in accordance with SQL's normal rules for Boolean combinations
of null values.
</para>
<para>
As with <token>EXISTS</token>, it's unwise to assume that the subquery will
be evaluated completely.
</para>
<synopsis>
(<replaceable>expression</replaceable> <optional>, <replaceable>expression</replaceable> ...</optional>) IN (<replaceable>subquery</replaceable>)
</synopsis>
<para>
The right-hand side of this form of <token>IN</token> is a parenthesized
subquery, which must return exactly as many columns as there are
expressions in the left-hand list. The left-hand expressions are
evaluated and compared row-wise to each row of the subquery result.
The result of <token>IN</token> is <quote>true</> if any equal subquery row is found.
The result is <quote>false</> if no equal row is found (including the special
case where the subquery returns no rows).
</para>
<para>
As usual, null values in the expressions or subquery rows are combined per
the normal rules of SQL Boolean expressions. Two rows are considered
equal if all their corresponding members are non-null and equal; the rows
are unequal if any corresponding members are non-null and unequal;
otherwise the result of that row comparison is unknown (null).
If all the row results are either unequal or null, with at least one null,
then the result of <token>IN</token> is null.
</para>
</sect2>
<sect2>
<title>NOT IN (scalar form)</title>
<synopsis>
<replaceable>expression</replaceable> NOT IN (<replaceable>value</replaceable><optional>, ...</optional>)
</synopsis>
<para>
The right-hand side of this form of <token>NOT IN</token> is a parenthesized list
of scalar expressions. The result is <quote>true</quote> if the left-hand expression's
result is unequal to all of the right-hand expressions. This is a shorthand
notation for
<synopsis>
<replaceable>expression</replaceable> &lt;&gt; <replaceable>value1</replaceable>
AND
<replaceable>expression</replaceable> &lt;&gt; <replaceable>value2</replaceable>
AND
...
</synopsis>
Note that if the left-hand expression yields null, or if there are
no equal right-hand values and at least one right-hand expression yields
null, the result of the <token>NOT IN</token> construct will be null, not true
as one might naively expect.
This is in accordance with SQL's normal rules for Boolean combinations
of null values.
</para>
<tip>
<para>
<literal>x NOT IN y</literal> is equivalent to <literal>NOT (x IN y)</literal> in all
cases. However, null values are much more likely to trip up the novice when
working with <token>NOT IN</token> than when working with <token>IN</token>.
It's best to express your condition positively if possible.
</para>
</tip>
</sect2>
<sect2>
<title>NOT IN (subquery form)</title>
<synopsis>
<replaceable>expression</replaceable> NOT IN (<replaceable>subquery</replaceable>)
</synopsis>
<para>
The right-hand side of this form of <token>NOT IN</token> is a parenthesized
subquery, which must return exactly one column. The left-hand expression
is evaluated and compared to each row of the subquery result.
The result of <token>NOT IN</token> is <quote>true</> if only unequal subquery rows
are found (including the special case where the subquery returns no rows).
The result is <quote>false</> if any equal row is found.
</para>
<para>
Note that if the left-hand expression yields null, or if there are
no equal right-hand values and at least one right-hand row yields
null, the result of the <token>NOT IN</token> construct will be null, not true.
This is in accordance with SQL's normal rules for Boolean combinations
of null values.
</para>
<para>
As with <token>EXISTS</token>, it's unwise to assume that the subquery will
be evaluated completely.
</para>
<synopsis>
(<replaceable>expression</replaceable> <optional>, <replaceable>expression</replaceable> ...</optional>) NOT IN (<replaceable>subquery</replaceable>)
</synopsis>
<para>
The right-hand side of this form of <token>NOT IN</token> is a parenthesized
subquery, which must return exactly as many columns as there are
expressions in the left-hand list. The left-hand expressions are
evaluated and compared row-wise to each row of the subquery result.
The result of <token>NOT IN</token> is <quote>true</> if only unequal subquery rows
are found (including the special case where the subquery returns no rows).
The result is <quote>false</> if any equal row is found.
</para>
<para>
As usual, null values in the expressions or subquery rows are combined per
the normal rules of SQL Boolean expressions. Two rows are considered
equal if all their corresponding members are non-null and equal; the rows
are unequal if any corresponding members are non-null and unequal;
otherwise the result of that row comparison is unknown (null).
If all the row results are either unequal or null, with at least one null,
then the result of <token>NOT IN</token> is null.
</para>
</sect2>
<sect2>
<title>ANY/SOME</title>
<synopsis>
<replaceable>expression</replaceable> <replaceable>operator</replaceable> ANY (<replaceable>subquery</replaceable>)
<replaceable>expression</replaceable> <replaceable>operator</replaceable> SOME (<replaceable>subquery</replaceable>)
</synopsis>
<para>
The right-hand side of this form of <token>ANY</token> is a parenthesized
subquery, which must return exactly one column. The left-hand expression
is evaluated and compared to each row of the subquery result using the
given <replaceable>operator</replaceable>, which must yield a Boolean
result.
The result of <token>ANY</token> is <quote>true</> if any true result is obtained.
The result is <quote>false</> if no true result is found (including the special
case where the subquery returns no rows).
</para>
<para>
<token>SOME</token> is a synonym for <token>ANY</token>.
<token>IN</token> is equivalent to <literal>= ANY</literal>.
</para>
<para>
Note that if there are no successes and at least one right-hand row yields
null for the operator's result, the result of the <token>ANY</token> construct
will be null, not false.
This is in accordance with SQL's normal rules for Boolean combinations
of null values.
</para>
<para>
As with <token>EXISTS</token>, it's unwise to assume that the subquery will
be evaluated completely.
</para>
<synopsis>
(<replaceable>expression</replaceable> <optional>, <replaceable>expression</replaceable> ...</optional>) <replaceable>operator</> ANY (<replaceable>subquery</replaceable>)
(<replaceable>expression</replaceable> <optional>, <replaceable>expression</replaceable> ...</optional>) <replaceable>operator</> SOME (<replaceable>subquery</replaceable>)
</synopsis>
<para>
The right-hand side of this form of <token>ANY</token> is a parenthesized
subquery, which must return exactly as many columns as there are
expressions in the left-hand list. The left-hand expressions are
evaluated and compared row-wise to each row of the subquery result,
using the given <replaceable>operator</replaceable>. Presently,
only <literal>=</literal> and <literal>&lt;&gt;</literal> operators are allowed
in row-wise <token>ANY</token> queries.
The result of <token>ANY</token> is <quote>true</> if any equal or unequal row is
found, respectively.
The result is <quote>false</> if no such row is found (including the special
case where the subquery returns no rows).
</para>
<para>
As usual, null values in the expressions or subquery rows are combined per
the normal rules of SQL Boolean expressions. Two rows are considered
equal if all their corresponding members are non-null and equal; the rows
are unequal if any corresponding members are non-null and unequal;
otherwise the result of that row comparison is unknown (null).
If there is at least one null row result, then the result of <token>ANY</token>
cannot be false; it will be true or null.
</para>
</sect2>
<sect2>
<title>ALL</title>
<synopsis>
<replaceable>expression</replaceable> <replaceable>operator</replaceable> ALL (<replaceable>subquery</replaceable>)
</synopsis>
<para>
The right-hand side of this form of <token>ALL</token> is a parenthesized
subquery, which must return exactly one column. The left-hand expression
is evaluated and compared to each row of the subquery result using the
given <replaceable>operator</replaceable>, which must yield a Boolean
result.
The result of <token>ALL</token> is <quote>true</> if all rows yield true
(including the special case where the subquery returns no rows).
The result is <quote>false</> if any false result is found.
</para>
<para>
<token>NOT IN</token> is equivalent to <literal>&lt;&gt; ALL</literal>.
</para>
<para>
Note that if there are no failures but at least one right-hand row yields
null for the operator's result, the result of the <token>ALL</token> construct
will be null, not true.
This is in accordance with SQL's normal rules for Boolean combinations
of null values.
</para>
<para>
As with <token>EXISTS</token>, it's unwise to assume that the subquery will
be evaluated completely.
</para>
<synopsis>
(<replaceable>expression</replaceable> <optional>, <replaceable>expression</replaceable> ...</optional>) <replaceable>operator</replaceable> ALL (<replaceable>subquery</replaceable>)
</synopsis>
<para>
The right-hand side of this form of <token>ALL</token> is a parenthesized
subquery, which must return exactly as many columns as there are
expressions in the left-hand list. The left-hand expressions are
evaluated and compared row-wise to each row of the subquery result,
using the given <replaceable>operator</replaceable>. Presently,
only <literal>=</literal> and <literal>&lt;&gt;</literal> operators are allowed
in row-wise <token>ALL</token> queries.
The result of <token>ALL</token> is <quote>true</> if all subquery rows are equal
or unequal, respectively (including the special
case where the subquery returns no rows).
The result is <quote>false</> if any row is found to be unequal or equal,
respectively.
</para>
<para>
As usual, null values in the expressions or subquery rows are combined per
the normal rules of SQL Boolean expressions. Two rows are considered
equal if all their corresponding members are non-null and equal; the rows
are unequal if any corresponding members are non-null and unequal;
otherwise the result of that row comparison is unknown (null).
If there is at least one null row result, then the result of <token>ALL</token>
cannot be true; it will be false or null.
</para>
</sect2>
<sect2>
<title>Row-wise Comparison</title>
<synopsis>
(<replaceable>expression</replaceable> <optional>, <replaceable>expression</replaceable> ...</optional>) <replaceable>operator</replaceable> (<replaceable>subquery</replaceable>)
(<replaceable>expression</replaceable> <optional>, <replaceable>expression</replaceable> ...</optional>) <replaceable>operator</replaceable> (<replaceable>expression</replaceable> <optional>, <replaceable>expression</replaceable> ...</optional>)
</synopsis>
<para>
The left-hand side is a list of scalar expressions. The right-hand side
can be either a list of scalar expressions of the same length, or a
parenthesized subquery, which must return exactly as many columns as there
are expressions on the left-hand side. Furthermore, the subquery cannot
return more than one row. (If it returns zero rows, the result is taken to
be null.) The left-hand side is evaluated and compared row-wise to the
single subquery result row, or to the right-hand expression list.
Presently, only <literal>=</literal> and <literal>&lt;&gt;</literal> operators are allowed
in row-wise comparisons.
The result is <quote>true</> if the two rows are equal or unequal, respectively.
</para>
<para>
As usual, null values in the expressions or subquery rows are combined per
the normal rules of SQL Boolean expressions. Two rows are considered
equal if all their corresponding members are non-null and equal; the rows
are unequal if any corresponding members are non-null and unequal;
otherwise the result of the row comparison is unknown (null).
</para>
</sect2>
</sect1>
</chapter>
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