Add mention of the SERIAL data type.
Change claim of "no limit" on maximum date for datetime type to more realistic 1465001 AD. Thanks Tatsuo for pointing this out :) Clean up markup.
This commit is contained in:
Thomas G. Lockhart
parent
edadec91f7
commit
3103a05c64
@ -3,26 +3,30 @@
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<Abstract>
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<Para>
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Describes the built-in data types available in <ProductName>Postgres</ProductName>.
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Describes the built-in data types available in
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<ProductName>Postgres</ProductName>.
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</Para>
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</Abstract>
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<Para>
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<ProductName>Postgres</ProductName> has a rich set of native data types available to users.
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<ProductName>Postgres</ProductName> has a rich set of native data
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types available to users.
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Users may add new types to <ProductName>Postgres</ProductName> using the
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<Command>define type</Command>
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command described elsewhere.
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<Para>
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In the context of data types, the following sections will discuss SQL standards
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compliance, porting issues, and usage.
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In the context of data types, the following sections will discuss
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<acronym>SQL</acronym> standards compliance, porting issues, and usage.
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Some <ProductName>Postgres</ProductName> types correspond directly to SQL92-compatible types. In other
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cases, data types defined by SQL92 syntax are mapped directly
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Some <ProductName>Postgres</ProductName> types correspond directly to
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<acronym>SQL92</acronym>-compatible types. In other
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cases, data types defined by <acronym>SQL92</acronym> syntax are mapped directly
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into native <ProductName>Postgres</ProductName> types.
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Many of the built-in types have obvious external formats. However, several
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types are either unique to <ProductName>Postgres</ProductName>, such as open and closed paths, or have
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types are either unique to <ProductName>Postgres</ProductName>,
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such as open and closed paths, or have
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several possibilities for formats, such as date and time types.
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</Para>
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@ -94,6 +98,11 @@ several possibilities for formats, such as date and time types.
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<ENTRY>numeric(p,s)</ENTRY>
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<ENTRY>exact numeric for p == 9, s = 0</ENTRY>
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</ROW>
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<ROW>
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<ENTRY>int8</ENTRY>
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<ENTRY></ENTRY>
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<ENTRY>signed 8-byte integer</ENTRY>
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</ROW>
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<ROW>
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<ENTRY>line</ENTRY>
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<ENTRY></ENTRY>
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@ -124,6 +133,11 @@ several possibilities for formats, such as date and time types.
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<ENTRY></ENTRY>
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<ENTRY>closed geometric path in 2D plane</ENTRY>
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</ROW>
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<ROW>
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<ENTRY>serial</ENTRY>
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<ENTRY></ENTRY>
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<ENTRY>unique id for indexing and cross-reference</ENTRY>
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</ROW>
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<ROW>
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<ENTRY>time</ENTRY>
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<ENTRY>time</ENTRY>
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@ -188,14 +202,16 @@ several possibilities for formats, such as date and time types.
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</Para>
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<Para>
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<ProductName>Postgres</ProductName> has features at the forefront of ORDBMS development. In addition to
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SQL3 conformance, substantial portions of SQL92 are also supported.
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Although we strive for SQL92 compliance, there are some aspects of the standard
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<ProductName>Postgres</ProductName> has features at the forefront of
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<acronym>ORDBMS</acronym> development. In addition to
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<acronym>SQL3</acronym> conformance, substantial portions
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of <acronym>SQL92</acronym> are also supported.
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Although we strive for <acronym>SQL92</acronym> compliance,
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there are some aspects of the standard
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which are ill considered and which should not live through subsequent standards.
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<ProductName>Postgres</ProductName> will not make great efforts to conform to these aspects;
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however, these
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tend to apply in little-used or obsure cases, and a typical user is not likely to
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run into them.
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<ProductName>Postgres</ProductName> will not make great efforts to
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conform to these features; however, these tend to apply in little-used
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or obsure cases, and a typical user is not likely to run into them.
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<Para>
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Most of the input and output functions corresponding to the
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@ -218,8 +234,9 @@ the original input.
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The original <ProductName>Postgres</ProductName> v4.2 code received from
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Berkeley rounded all double precision floating point results to six digits for
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output. Starting with v6.1, floating point numbers are allowed to retain
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most of the intrinsic precision of the type (typically 15 digits for doubles, 6 digits
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for 4-byte floats). Other types with underlying floating point fields (e.g. geometric
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most of the intrinsic precision of the type (typically 15 digits for doubles,
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6 digits for 4-byte floats).
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Other types with underlying floating point fields (e.g. geometric
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types) carry similar precision.
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</note>
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</Para>
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@ -245,6 +262,18 @@ floating point numbers.
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</ROW>
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</THEAD>
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<TBODY>
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<ROW>
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<ENTRY>float4</ENTRY>
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<ENTRY>4 bytes</ENTRY>
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<ENTRY>Variable-precision</ENTRY>
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<ENTRY>6 decimal places</ENTRY>
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</ROW>
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<ROW>
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<ENTRY>float8</ENTRY>
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<ENTRY>8 bytes</ENTRY>
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<ENTRY>Variable-precision</ENTRY>
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<ENTRY>15 decimal places</ENTRY>
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</ROW>
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<ROW>
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<ENTRY>int2</ENTRY>
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<ENTRY>2 bytes</ENTRY>
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@ -264,27 +293,64 @@ floating point numbers.
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<ENTRY>+/- > 18 decimal places</ENTRY>
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</ROW>
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<ROW>
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<ENTRY>float4</ENTRY>
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<ENTRY>serial</ENTRY>
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<ENTRY>4 bytes</ENTRY>
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<ENTRY>Variable-precision</ENTRY>
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<ENTRY>6 decimal places</ENTRY>
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</ROW>
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<ROW>
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<ENTRY>float8</ENTRY>
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<ENTRY>8 bytes</ENTRY>
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<ENTRY>Variable-precision</ENTRY>
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<ENTRY>15 decimal places</ENTRY>
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<ENTRY>Identifer or cross-reference</ENTRY>
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<ENTRY>0 to +2147483647</ENTRY>
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</ROW>
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</TBODY>
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</TGROUP>
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</TABLE>
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</Para>
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<para>
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The numeric types have a full set of corresponding arithmetic operators and
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functions. Refer to <xref linkend="math-opers" endterm="math-opers">
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and <xref linkend="math-funcs" endterm="math-funcs"> for more information.
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<para>
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The <type>serial</type> type is a special-case type constructed by
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<productname>Postgres</productname> from other existing components.
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It is typically used to create unique identifiers for table entries.
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In the current implementation, specifying
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<programlisting>
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CREATE TABLE <replaceable class="parameter">tablename</replaceable> (<replaceable class="parameter">colname</replaceable> SERIAL);
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</programlisting>
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is equivalent to specifying:
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<programlisting>
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CREATE SEQUENCE <replaceable class="parameter">tablename</replaceable>_<replaceable class="parameter">colname</replaceable>_seq;
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CREATE TABLE <replaceable class="parameter">tablename</replaceable>
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(<replaceable class="parameter">colname</replaceable> INT4 DEFAULT nextval('<replaceable class="parameter">tablename</replaceable>_<replaceable class="parameter">colname</replaceable>_seq');
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CREATE UNIQUE INDEX <replaceable class="parameter">tablename</replaceable>_<replaceable class="parameter">colname</replaceable>_key on <replaceable class="parameter">tablename</replaceable> (<replaceable class="parameter">colname</replaceable>);
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</programlisting>
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<caution>
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<para>
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The implicit sequence created for the <type>serial</type> type will
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<emphasis>not</emphasis> be automatically removed when the table is dropped.
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So, the following commands executed in order will likely fail:
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<programlisting>
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CREATE TABLE <replaceable class="parameter">tablename</replaceable> (<replaceable class="parameter">colname</replaceable> SERIAL);
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DROP TABLE <replaceable class="parameter">tablename</replaceable>;
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CREATE TABLE <replaceable class="parameter">tablename</replaceable> (<replaceable class="parameter">colname</replaceable> SERIAL);
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</programlisting>
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The sequence will remain in the database until explicitly dropped using
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<command>DROP SEQUENCE</command>.
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</caution>
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<Para>
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The <FirstTerm>exact numerics</FirstTerm> <Type>decimal</Type> and <Type>numeric</Type>
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have fully implemented syntax but currently (<ProductName>Postgres</ProductName> v6.3)
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The <FirstTerm>exact numerics</FirstTerm> <Type>decimal</Type> and
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<Type>numeric</Type>
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have fully implemented syntax but currently
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(<ProductName>Postgres</ProductName> v6.4)
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support only a small range of precision and/or range values.
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The <type>int8</type> type may not be available on all platforms.
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The <type>int8</type> type may not be available on all platforms since
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it relies on compiler support for this.
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</Para>
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</Sect1>
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@ -293,9 +359,12 @@ The <type>int8</type> type may not be available on all platforms.
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<Title>Monetary Type</Title>
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<Para>
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The <Type>money</Type> type supports US-style currency with fixed decimal point representation.
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If <ProductName>Postgres</ProductName> is compiled with USE_LOCALE then the money type
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should use the monetary conventions defined for locale(7).
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The <Type>money</Type> type supports US-style currency with
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fixed decimal point representation.
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If <ProductName>Postgres</ProductName> is compiled with USE_LOCALE
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then the money type
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should use the monetary conventions defined for
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<citetitle>locale(7)</citetitle>.
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<Para>
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<TABLE TOCENTRY="1">
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@ -323,11 +392,12 @@ should use the monetary conventions defined for locale(7).
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</Para>
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<Para>
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The <FirstTerm>numeric</FirstTerm>
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<type>numeric</type>
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should eventually replace the money type. It has a
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fully implemented syntax but currently (<ProductName>Postgres</ProductName> v6.3)
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support only a small range of precision and/or range values and cannot substitute for
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the money type.
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fully implemented syntax but currently
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(<ProductName>Postgres</ProductName> v6.4)
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support only a small range of precision and/or range values
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and cannot adequately substitute for the money type.
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</Para>
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</Sect1>
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@ -336,9 +406,11 @@ the money type.
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<Title>Character Types</Title>
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<Para>
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<Acronym>SQL92</Acronym> defines two primary character types: <Type>char</Type> and
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<Type>varchar</Type>. <ProductName>Postgres</ProductName> supports these types, in
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addition to the more general <Type>text</Type> type, which unlike <Type>varchar</Type>
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<Acronym>SQL92</Acronym> defines two primary character types:
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<Type>char</Type> and <Type>varchar</Type>.
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<ProductName>Postgres</ProductName> supports these types, in
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addition to the more general <Type>text</Type> type,
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which unlike <Type>varchar</Type>
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does not require an upper
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limit to be declared on the size of the field.
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</Para>
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@ -360,13 +432,13 @@ limit to be declared on the size of the field.
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<ROW>
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<ENTRY>char</ENTRY>
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<ENTRY>1 byte</ENTRY>
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<ENTRY>SQL92-compatible</ENTRY>
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<ENTRY><acronym>SQL92</acronym>-compatible</ENTRY>
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<ENTRY>Single character</ENTRY>
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</ROW>
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<ROW>
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<ENTRY>char(n)</ENTRY>
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<ENTRY>(4+n) bytes</ENTRY>
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<ENTRY>SQL92-compatible</ENTRY>
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<ENTRY><acronym>SQL92</acronym>-compatible</ENTRY>
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<ENTRY>Fixed-length blank padded</ENTRY>
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</ROW>
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<ROW>
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@ -378,7 +450,7 @@ limit to be declared on the size of the field.
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<ROW>
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<ENTRY>varchar(n)</ENTRY>
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<ENTRY>(4+n) bytes</ENTRY>
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<ENTRY>SQL92-compatible</ENTRY>
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<ENTRY><acronym>SQL92</acronym>-compatible</ENTRY>
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<ENTRY>Variable-length with limit</ENTRY>
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</ROW>
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</TBODY>
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@ -387,10 +459,14 @@ limit to be declared on the size of the field.
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</Para>
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<Para>
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There is currently one other fixed-length character type. The <Type>name</Type> type
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only has one purpose and that is to provide <ProductName>Postgres</ProductName> with a
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special type to use for internal names. It is not intended for use by the general user.
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It's length is currently defined as 32 chars but should be reference using NAMEDATALEN.
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There is one other fixed-length character type.
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The <Type>name</Type> type
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only has one purpose and that is to provide
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<ProductName>Postgres</ProductName> with a
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special type to use for internal names.
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It is not intended for use by the general user.
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It's length is currently defined as 32 chars
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but should be reference using NAMEDATALEN.
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This is set at compile time and may change in a future release.
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</Para>
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@ -423,10 +499,13 @@ This is set at compile time and may change in a future release.
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<Title>Date/Time Types</Title>
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<Para>
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There are two fundamental kinds of date and time measurements: clock time and time interval.
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There are two fundamental kinds of date and time measurements:
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clock time and time interval.
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Both quantities have continuity and smoothness, as does time itself.
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<ProductName>Postgres</ProductName> supplies two primary user-oriented date and time types,
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<Type>datetime</Type> and timespan, as well as the related SQL92 types date and time.
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<ProductName>Postgres</ProductName> supplies two primary user-oriented
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date and time types,
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<Type>datetime</Type> and timespan, as well as
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the related <acronym>SQL92</acronym> types date and time.
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</Para>
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<Para>
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@ -458,7 +537,7 @@ for historical reasons.
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<ROW>
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<ENTRY>date</ENTRY>
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<ENTRY>4 bytes</ENTRY>
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<ENTRY>SQL92 type</ENTRY>
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<ENTRY><acronym>SQL92</acronym> type</ENTRY>
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<ENTRY>wide range</ENTRY>
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</ROW>
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<ROW>
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@ -470,7 +549,7 @@ for historical reasons.
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<ROW>
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<ENTRY>interval</ENTRY>
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<ENTRY>12 bytes</ENTRY>
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<ENTRY>SQL92 type</ENTRY>
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<ENTRY><acronym>SQL92</acronym> type</ENTRY>
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<ENTRY>equivalent to timespan</ENTRY>
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</ROW>
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<ROW>
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@ -482,7 +561,7 @@ for historical reasons.
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<ROW>
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<ENTRY>time</ENTRY>
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<ENTRY>4 bytes</ENTRY>
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<ENTRY>SQL92 type</ENTRY>
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<ENTRY><acronym>SQL92</acronym> type</ENTRY>
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<ENTRY>wide range</ENTRY>
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</ROW>
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<ROW>
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@ -494,7 +573,7 @@ for historical reasons.
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<ROW>
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<ENTRY>timestamp</ENTRY>
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<ENTRY>4 bytes</ENTRY>
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<ENTRY>SQL92 type</ENTRY>
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<ENTRY><acronym>SQL92</acronym> type</ENTRY>
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<ENTRY>limited range</ENTRY>
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</ROW>
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</TBODY>
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@ -525,19 +604,19 @@ for historical reasons.
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<ROW>
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<ENTRY>date</ENTRY>
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<ENTRY>4713 BC</ENTRY>
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<ENTRY>no limit</ENTRY>
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<ENTRY>32767 AD</ENTRY>
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<ENTRY>1 day</ENTRY>
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</ROW>
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<ROW>
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<ENTRY>datetime</ENTRY>
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<ENTRY>4713 BC</ENTRY>
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<ENTRY>no limit</ENTRY>
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<ENTRY>1465001 AD</ENTRY>
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<ENTRY>1 microsec to 14 digits</ENTRY>
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</ROW>
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<ROW>
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<ENTRY>interval</ENTRY>
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<ENTRY>no limit</ENTRY>
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<ENTRY>no limit</ENTRY>
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<ENTRY>-178000000 years</ENTRY>
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<ENTRY>178000000 years</ENTRY>
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<ENTRY>1 microsec</ENTRY>
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</ROW>
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<ROW>
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@ -554,8 +633,8 @@ for historical reasons.
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</ROW>
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<ROW>
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<ENTRY>timespan</ENTRY>
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<ENTRY>no limit</ENTRY>
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<ENTRY>no limit</ENTRY>
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<ENTRY>-178000000 years</ENTRY>
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<ENTRY>178000000 years</ENTRY>
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<ENTRY>1 microsec (14 digits)</ENTRY>
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</ROW>
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<ROW>
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@ -573,26 +652,33 @@ for historical reasons.
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<ProductName>Postgres</ProductName> endevours to be compatible with
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<Acronym>SQL92</Acronym> definitions for typical usage.
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The <Acronym>SQL92</Acronym> standard has an odd mix of date and
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time types and capabilities. For example, although the date type does not have an associated time zone, the
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time type can. The default time zone is specified as a constant offset from GMT/UTC;
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however, time zones in the real world can have no meaning unless associated with a
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date as well
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time types and capabilities. For example, although the date type
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does not have an associated time zone, the
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time type can. The default time zone is specified as a constant offset
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from GMT/UTC;
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however, time zones in the real world can have no meaning unless
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associated with a date as well
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as a time since the offset will vary through the year.
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<Para>
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To obviate these difficulties, <ProductName>Postgres</ProductName> associates time zones
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only with date and time
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types which contain both date and time, and assumes local time for any type containing only
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date or time. Further, time zone support is derived from the underlying operating system
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time zone capabilities, and hence can handle daylight savings time and other expected behavior.
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To address these difficulties, <ProductName>Postgres</ProductName>
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associates time zones only with date and time
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types which contain both date and time,
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and assumes local time for any type containing only
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date or time. Further, time zone support is derived from
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the underlying operating system
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time zone capabilities, and hence can handle daylight savings time
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and other expected behavior.
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|
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<Para>
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In future releases, the number of date/time types will decrease, with the current
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implementation of <Type>datetime</Type> becoming <Type>timestamp</Type>, timespan becoming interval,
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and (possibly) abstime
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and reltime being deprecated in favor of <Type>timestamp</Type> and interval.
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The more arcane features
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of the date/time definitions from the <Acronym>SQL92</Acronym> standard are not likely to be pursued.
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In future releases, the number of date/time types will decrease,
|
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with the current implementation of
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<Type>datetime</Type> becoming <Type>timestamp</Type>,
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<Type>timespan</Type> becoming <Type>interval</Type>,
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and (possibly) <Type>abstime</Type> and <Type>reltime</Type>
|
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being deprecated in favor of <Type>timestamp</Type> and <Type>interval</Type>.
|
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The more arcane features of the date/time definitions from
|
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the <Acronym>SQL92</Acronym> standard are not likely to be pursued.
|
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</Para>
|
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|
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<Sect2>
|
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@ -600,7 +686,7 @@ of the date/time definitions from the <Acronym>SQL92</Acronym> standard are not
|
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|
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<Para>
|
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Output formats can be set to one of four styles:
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ISO-8601, SQL (Ingres), traditional
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ISO-8601, <acronym>SQL</acronym> (Ingres), traditional
|
||||
Postgres, and German.
|
||||
|
||||
<TABLE TOCENTRY="1">
|
||||
@ -621,7 +707,7 @@ Postgres, and German.
|
||||
<ENTRY>1997-12-17 07:37:16-08</ENTRY>
|
||||
</ROW>
|
||||
<ROW>
|
||||
<ENTRY>SQL</ENTRY>
|
||||
<ENTRY><acronym>SQL</acronym></ENTRY>
|
||||
<ENTRY>Traditional style</ENTRY>
|
||||
<ENTRY>12/17/1997 07:37:16.00 PST</ENTRY>
|
||||
</ROW>
|
||||
@ -641,8 +727,8 @@ Postgres, and German.
|
||||
</Para>
|
||||
|
||||
<Para>
|
||||
The SQL style has European and non-European (US) variants, which determines whether
|
||||
month follows day or vica versa.
|
||||
The <acronym>SQL</acronym> style has European and non-European (US) variants,
|
||||
which determines whether month follows day or vica versa.
|
||||
|
||||
<TABLE TOCENTRY="1">
|
||||
<TITLE><ProductName>Postgres</ProductName> Date Order Conventions</TITLE>
|
||||
@ -682,12 +768,14 @@ There are several ways to affect the appearance of date/time types:
|
||||
<ItemizedList Mark="bullet" Spacing="compact">
|
||||
<ListItem>
|
||||
<Para>
|
||||
The PGDATESTYLE environment variable used by the backend directly on postmaster startup.
|
||||
The PGDATESTYLE environment variable used by the backend directly
|
||||
on postmaster startup.
|
||||
</Para>
|
||||
</ListItem>
|
||||
<ListItem>
|
||||
<Para>
|
||||
The PGDATESTYLE environment variable used by the frontend libpq on session startup.
|
||||
The PGDATESTYLE environment variable used by the frontend libpq
|
||||
on session startup.
|
||||
</Para>
|
||||
</ListItem>
|
||||
<ListItem>
|
||||
@ -698,8 +786,10 @@ SET DateStyle <Acronym>SQL</Acronym> command.
|
||||
</ItemizedList>
|
||||
|
||||
<Para>
|
||||
For <ProductName>Postgres</ProductName> v6.3 (and earlier) the default date/time style is
|
||||
"non-European traditional Postgres". In future releases, the default may become ISO-8601, which alleviates
|
||||
For <ProductName>Postgres</ProductName> v6.4 (and earlier)
|
||||
the default date/time style is
|
||||
"non-European traditional Postgres".
|
||||
In future releases, the default may become ISO-8601, which alleviates
|
||||
date specification ambiguities and Y2K collation problems.
|
||||
</Para>
|
||||
|
||||
@ -709,9 +799,11 @@ date specification ambiguities and Y2K collation problems.
|
||||
<Title>Time Zones</Title>
|
||||
|
||||
<Para>
|
||||
<ProductName>Postgres</ProductName> obtains time zone support from the underlying operating system.
|
||||
All dates and times are stored internally in Universal Coordinated Time (UTC), alternately known as
|
||||
Greenwich Mean Time (GMT). Times are converted to local time on the database server before being
|
||||
<ProductName>Postgres</ProductName> obtains time zone support
|
||||
from the underlying operating system.
|
||||
All dates and times are stored internally in Universal Coordinated Time (UTC),
|
||||
alternately known as Greenwich Mean Time (GMT).
|
||||
Times are converted to local time on the database server before being
|
||||
sent to the client frontend, hence by default are in the server time zone.
|
||||
|
||||
<Para>
|
||||
@ -726,12 +818,14 @@ The TZ environment variable used by the backend directly
|
||||
</ListItem>
|
||||
<ListItem>
|
||||
<Para>
|
||||
The PGTZ environment variable set at the client used by libpq to send time zone information to the backend upon connection.
|
||||
The PGTZ environment variable set at the client used by libpq
|
||||
to send time zone information to the backend upon connection.
|
||||
</Para>
|
||||
</ListItem>
|
||||
<ListItem>
|
||||
<Para>
|
||||
<Command>set timezone</Command> <Acronym>SQL</Acronym> sets the time zone for the session.
|
||||
The <Acronym>SQL</Acronym> command <Command>SET TIME ZONE</Command>
|
||||
sets the time zone for the session.
|
||||
</Para>
|
||||
</ListItem>
|
||||
</ItemizedList>
|
||||
@ -747,21 +841,25 @@ the time zone becomes GMT (on most systems anyway).
|
||||
|
||||
<Para>
|
||||
General-use date and time is input using a wide range of
|
||||
styles, including ISO-compatible, SQL-compatible, traditional
|
||||
<ProductName>Postgres</ProductName>
|
||||
styles, including ISO-compatible, <acronym>SQL</acronym>-compatible,
|
||||
traditional <ProductName>Postgres</ProductName>
|
||||
and other permutations of date and time. In cases where interpretation
|
||||
can be ambiguous (quite possible with many traditional styles of date specification)
|
||||
<ProductName>Postgres</ProductName> uses a style setting to resolve the ambiguity.
|
||||
can be ambiguous (quite possible with many traditional styles of date
|
||||
specification) <ProductName>Postgres</ProductName> uses a style setting
|
||||
to resolve the ambiguity.
|
||||
</Para>
|
||||
|
||||
<Para>
|
||||
Most date and time types share code for data input. For those types
|
||||
the input can have any of a wide variety of styles. For numeric date representations,
|
||||
European and US conventions can differ, and the proper interpretation is obtained
|
||||
the input can have any of a wide variety of styles. For numeric date
|
||||
representations,
|
||||
European and US conventions can differ, and the proper interpretation
|
||||
is obtained
|
||||
by using the
|
||||
<Command>set datestyle</Command>
|
||||
command before entering data.
|
||||
Note that the style setting does not preclude use of various styles for input; it is
|
||||
Note that the style setting does not preclude use of various styles for input;
|
||||
it is
|
||||
used primarily to determine the output style and to resolve ambiguities.
|
||||
</Para>
|
||||
|
||||
@ -844,10 +942,11 @@ for it. `epoch' means Jan 1 00:00:00 1970 GMT.
|
||||
|
||||
<Para>
|
||||
General-use date and time is input using a wide range of
|
||||
styles, including ISO-compatible, SQL-compatible, traditional
|
||||
styles, including ISO-compatible, <acronym>SQL</acronym>-compatible, traditional
|
||||
<ProductName>Postgres</ProductName> (see section on "absolute time")
|
||||
and other permutations of date and time. Output styles can be ISO-compatible,
|
||||
SQL-compatible, or traditional <ProductName>Postgres</ProductName>, with the default set to be compatible
|
||||
<acronym>SQL</acronym>-compatible, or traditional
|
||||
<ProductName>Postgres</ProductName>, with the default set to be compatible
|
||||
with <ProductName>Postgres</ProductName> v6.0.
|
||||
</Para>
|
||||
|
||||
@ -881,13 +980,18 @@ translate time to the local time zone of the server.
|
||||
|
||||
<Para>
|
||||
General-use time span is input using a wide range of
|
||||
syntaxes, including ISO-compatible, SQL-compatible, traditional
|
||||
syntaxes, including ISO-compatible, <acronym>SQL</acronym>-compatible,
|
||||
traditional
|
||||
<ProductName>Postgres</ProductName> (see section on "relative time")
|
||||
and other permutations of time span. Output formats can be ISO-compatible,
|
||||
SQL-compatible, or traditional <ProductName>Postgres</ProductName>, with the default set to be <ProductName>Postgres</ProductName>-compatible.
|
||||
<acronym>SQL</acronym>-compatible, or traditional
|
||||
<ProductName>Postgres</ProductName>,
|
||||
with the default set to be <ProductName>Postgres</ProductName>-compatible.
|
||||
Months and years are a "qualitative" time interval, and are stored separately
|
||||
from the other "quantitative" time intervals such as day or hour. For date arithmetic,
|
||||
the qualitative time units are instantiated in the context of the relevant date or time.
|
||||
from the other "quantitative" time intervals such as day or hour.
|
||||
For date arithmetic,
|
||||
the qualitative time units are instantiated in the context of the
|
||||
relevant date or time.
|
||||
|
||||
<Para>
|
||||
Time span is specified with the following syntax:
|
||||
@ -908,7 +1012,8 @@ where
|
||||
<Title>abstime</Title>
|
||||
|
||||
<Para>
|
||||
Absolute time (abstime) is a limited-range (+/- 68 years) and limited-precision (1 sec)
|
||||
Absolute time (<type>abstime</type>) is a limited-range (+/- 68 years) and
|
||||
limited-precision (1 sec)
|
||||
date data type. <Type>datetime</Type> may be preferred, since it
|
||||
covers a larger range with greater precision.
|
||||
|
||||
@ -929,11 +1034,18 @@ where
|
||||
|
||||
<Para>
|
||||
Valid dates are from Dec 13 20:45:53 1901 GMT to Jan 19 03:14:04
|
||||
2038 GMT. As of Version 3.0, times are no longer read and written
|
||||
2038 GMT.
|
||||
|
||||
<note>
|
||||
<title>Historical Note</title>
|
||||
<para>
|
||||
As of Version 3.0, times are no longer read and written
|
||||
using Greenwich Mean Time; the input and output routines default to
|
||||
the local time zone.
|
||||
</note>
|
||||
|
||||
All special values allowed for <Type>datetime</Type> are also allowed for "absolute time".
|
||||
All special values allowed for <Type>datetime</Type> are also
|
||||
allowed for "absolute time".
|
||||
</Para>
|
||||
|
||||
</Sect2>
|
||||
@ -945,15 +1057,20 @@ All special values allowed for <Type>datetime</Type> are also allowed for "absol
|
||||
Relative time <Type>reltime</Type> is a limited-range (+/- 68 years)
|
||||
and limited-precision (1 sec) time span data type.
|
||||
<Type>timespan</Type> should be preferred, since it
|
||||
covers a larger range with greater precision and, more importantly, can distinguish between
|
||||
relative units (months and years) and quantitative units (days, hours, etc). Instead, reltime
|
||||
must force months to be exactly 30 days, so time arithmetic does not always work as expected.
|
||||
For example, adding one reltime year to abstime today does not produce today's date one year from
|
||||
covers a larger range with greater precision and, more importantly,
|
||||
can distinguish between
|
||||
relative units (months and years) and quantitative units (days, hours, etc).
|
||||
Instead, reltime
|
||||
must force months to be exactly 30 days, so time arithmetic does not
|
||||
always work as expected.
|
||||
For example, adding one reltime year to abstime today does not
|
||||
produce today's date one year from
|
||||
now, but rather a date 360 days from today.
|
||||
</Para>
|
||||
|
||||
<Para>
|
||||
<Type>reltime</Type> shares input and output routines with the other time span types.
|
||||
<Type>reltime</Type> shares input and output routines with the other
|
||||
time span types.
|
||||
The section on <Type>timespan</Type> covers this in more detail.
|
||||
</Para>
|
||||
|
||||
@ -966,12 +1083,14 @@ The section on <Type>timespan</Type> covers this in more detail.
|
||||
This is currently a limited-range absolute time which closely resembles the
|
||||
abstime
|
||||
data type. It shares the general input parser with the other date/time types.
|
||||
In future releases this type will absorb the capabilities of the <Type>datetime</Type> type
|
||||
and will move toward SQL92 compliance.
|
||||
In future releases this type will absorb the capabilities of the
|
||||
<Type>datetime</Type> type
|
||||
and will move toward <acronym>SQL92</acronym> compliance.
|
||||
</Para>
|
||||
|
||||
<Para>
|
||||
<Type>timestamp</Type> is specified using the same syntax as for <Type>datetime</Type>.
|
||||
<Type>timestamp</Type> is specified using the same syntax as for
|
||||
<Type>datetime</Type>.
|
||||
</Para>
|
||||
</Sect2>
|
||||
|
||||
@ -980,8 +1099,8 @@ and will move toward SQL92 compliance.
|
||||
|
||||
<Para>
|
||||
<Type>interval</Type> is an <Acronym>SQL92</Acronym> data type which is
|
||||
currently mapped to the <Type>timespan</Type> <ProductName>Postgres</ProductName>
|
||||
data type.
|
||||
currently mapped to the <Type>timespan</Type>
|
||||
<ProductName>Postgres</ProductName> data type.
|
||||
</Para>
|
||||
</Sect2>
|
||||
|
||||
@ -1009,9 +1128,12 @@ Special abstime values such as
|
||||
<Para>
|
||||
<ProductName>Postgres</ProductName> supports <Type>bool</Type> as
|
||||
the <Acronym>SQL3</Acronym> boolean type.
|
||||
<Type>bool</Type> can have one of only two states: 'true' or 'false'. A third state, 'unknown', is not
|
||||
implemented and is not suggested in <Acronym>SQL3</Acronym>; <Acronym>NULL</Acronym> is an
|
||||
effective substitute. <Type>bool</Type> can be used in any boolean expression, and boolean expressions
|
||||
<Type>bool</Type> can have one of only two states: 'true' or 'false'.
|
||||
A third state, 'unknown', is not
|
||||
implemented and is not suggested in <Acronym>SQL3</Acronym>;
|
||||
<Acronym>NULL</Acronym> is an
|
||||
effective substitute. <Type>bool</Type> can be used in any boolean expression,
|
||||
and boolean expressions
|
||||
always evaluate to a result compatible with this type.
|
||||
|
||||
<Para>
|
||||
@ -1051,7 +1173,8 @@ always evaluate to a result compatible with this type.
|
||||
<Title>Geometric Types</Title>
|
||||
|
||||
<Para>
|
||||
Geometric types represent two-dimensional spatial objects. The most fundamental type,
|
||||
Geometric types represent two-dimensional spatial objects.
|
||||
The most fundamental type,
|
||||
the point, forms the basis for all of the other types.
|
||||
</Para>
|
||||
|
||||
@ -1124,7 +1247,8 @@ the point, forms the basis for all of the other types.
|
||||
|
||||
<Para>
|
||||
A rich set of functions and operators is available to perform various geometric
|
||||
operations such as scaling, translation, rotation, and determining intersections.
|
||||
operations such as scaling, translation, rotation, and determining
|
||||
intersections.
|
||||
</Para>
|
||||
|
||||
<Sect2>
|
||||
@ -1222,9 +1346,11 @@ where
|
||||
</ProgramListing>
|
||||
Paths are output using the first syntax.
|
||||
Note that <ProductName>Postgres</ProductName> versions prior to
|
||||
v6.1 used a format for paths which had a single leading parenthesis, a "closed" flag,
|
||||
v6.1 used a format for paths which had a single leading parenthesis,
|
||||
a "closed" flag,
|
||||
an integer count of the number of points, then the list of points followed by a
|
||||
closing parenthesis. The built-in function <Function>upgradepath</Function> is supplied to convert
|
||||
closing parenthesis.
|
||||
The built-in function <Function>upgradepath</Function> is supplied to convert
|
||||
paths dumped and reloaded from pre-v6.1 databases.
|
||||
</Para>
|
||||
</Sect2>
|
||||
@ -1234,9 +1360,8 @@ paths dumped and reloaded from pre-v6.1 databases.
|
||||
|
||||
<Para>
|
||||
Polygons are represented by sets of points. Polygons should probably be
|
||||
considered
|
||||
equivalent to closed paths, but are stored differently and have their own
|
||||
set of support routines.
|
||||
considered equivalent to closed paths, but are stored differently
|
||||
and have their own set of support routines.
|
||||
</Para>
|
||||
|
||||
<Para>
|
||||
@ -1254,7 +1379,8 @@ where
|
||||
Polygons are output using the first syntax.
|
||||
Note that <ProductName>Postgres</ProductName> versions prior to
|
||||
v6.1 used a format for polygons which had a single leading parenthesis, the list
|
||||
of x-axis coordinates, the list of y-axis coordinates, followed by a closing parenthesis.
|
||||
of x-axis coordinates, the list of y-axis coordinates,
|
||||
followed by a closing parenthesis.
|
||||
The built-in function <Function>upgradepoly</Function> is supplied to convert
|
||||
polygons dumped and reloaded from pre-v6.1 databases.
|
||||
</Para>
|
||||
|
||||
Loading…
x
Reference in New Issue
Block a user