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Give the full syntax rules for subscripting and field selection in the

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proper place, namely the syntax discussion of value expressions.
This commit is contained in:
Tom Lane 2003-11-04 19:18:15 +00:00
parent c58083a941
commit 64caee7548
1 changed files with 94 additions and 20 deletions
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doc/src/sgml/syntax.sgml
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@ -1,5 +1,5 @@
<!--
$Header: /cvsroot/pgsql/doc/src/sgml/syntax.sgml,v 1.86 2003/11/04 09:55:39 petere Exp $
$Header: /cvsroot/pgsql/doc/src/sgml/syntax.sgml,v 1.87 2003/11/04 19:18:15 tgl Exp $
-->
<chapter id="sql-syntax">
@ -185,7 +185,7 @@ UPDATE "my_table" SET "a" = 5;
<para>
Quoted identifiers can contain any character other than a double
quote itself. To include a double quote, write two double quotes.
quote itself. (To include a double quote, write two double quotes.)
This allows constructing table or column names that would
otherwise not be possible, such as ones containing spaces or
ampersands. The length limitation still applies.
@ -449,7 +449,7 @@ CAST ( '<replaceable>string</replaceable>' AS <replaceable>type</replaceable> )
</indexterm>
<para>
An operator is a sequence of up to <symbol>NAMEDATALEN</symbol>-1
An operator name is a sequence of up to <symbol>NAMEDATALEN</symbol>-1
(63 by default) characters from the following list:
<literallayout>
+ - * / &lt; &gt; = ~ ! @ # % ^ &amp; | ` ?
@ -855,6 +855,18 @@ SELECT 3 OPERATOR(pg_catalog.+) 4;
</para>
</listitem>
<listitem>
<para>
A subscripted expression.
</para>
</listitem>
<listitem>
<para>
A field selection expression.
</para>
</listitem>
<listitem>
<para>
An operator invocation.
@ -928,31 +940,18 @@ SELECT 3 OPERATOR(pg_catalog.+) 4;
<synopsis>
<replaceable>correlation</replaceable>.<replaceable>columnname</replaceable>
</synopsis>
or
<synopsis>
<replaceable>correlation</replaceable>.<replaceable>columnname</replaceable>[<replaceable>subscript</replaceable>]
</synopsis>
(Here, the brackets <literal>[ ]</literal> are meant to appear literally.)
</para>
<para>
<replaceable>correlation</replaceable> is the name of a
table (possibly qualified), or an alias for a table defined by means of a
<literal>FROM</literal> clause, or
table (possibly qualified with a schema name), or an alias for a table
defined by means of a <literal>FROM</literal> clause, or one of
the key words <literal>NEW</literal> or <literal>OLD</literal>.
(<literal>NEW</literal> and <literal>OLD</literal> can only appear in rewrite rules,
while other correlation names can be used in any SQL statement.)
The correlation name and separating dot may be omitted if the column name
is unique across all the tables being used in the current query. (See also <xref linkend="queries">.)
</para>
<para>
If <replaceable>column</replaceable> is of an array type, then the
optional <replaceable>subscript</replaceable> selects a specific
element or elements in the array. If no subscript is provided, then the
whole array is selected. (See <xref linkend="arrays"> for more about
arrays.)
</para>
</sect2>
<sect2>
@ -995,6 +994,81 @@ CREATE FUNCTION dept(text) RETURNS dept
</para>
</sect2>
<sect2>
<title>Subscripts</title>
<indexterm>
<primary>subscript</primary>
</indexterm>
<para>
If an expression yields a value of an array type, then a specific
element of the array value can be extracted by writing
<synopsis>
<replaceable>expression</replaceable>[<replaceable>subscript</replaceable>]
</synopsis>
or multiple adjacent elements (an <quote>array slice</>) can be extracted
by writing
<synopsis>
<replaceable>expression</replaceable>[<replaceable>lower_subscript</replaceable>:<replaceable>upper_subscript</replaceable>]
</synopsis>
(Here, the brackets <literal>[ ]</literal> are meant to appear literally.)
Each <replaceable>subscript</replaceable> is itself an expression,
which must yield an integer value.
</para>
<para>
In general the array <replaceable>expression</replaceable> must be
parenthesized, but the parentheses may be omitted when the expression
to be subscripted is just a column reference or positional parameter.
Also, multiple subscripts can be concatenated when the original array
is multi-dimensional.
For example,
<programlisting>
mytable.arraycolumn[4]
mytable.two_d_column[17][34]
$1[10:42]
(arrayfunction(a,b))[42]
</programlisting>
The parentheses in the last example are required.
See <xref linkend="arrays"> for more about arrays.
</para>
</sect2>
<sect2>
<title>Field Selection</title>
<indexterm>
<primary>field selection</primary>
</indexterm>
<para>
If an expression yields a value of a composite type (row type), then a
specific field of the row can be extracted by writing
<synopsis>
<replaceable>expression</replaceable>.<replaceable>fieldname</replaceable>
</synopsis>
</para>
<para>
In general the row <replaceable>expression</replaceable> must be
parenthesized, but the parentheses may be omitted when the expression
to be selected from is just a table reference or positional parameter.
For example,
<programlisting>
mytable.mycolumn
$1.somecolumn
(rowfunction(a,b)).col3
</programlisting>
(Thus, a qualified column reference is actually just a special case
of the field selection syntax.)
</para>
</sect2>
<sect2>
<title>Operator Invocations</title>
@ -1013,7 +1087,7 @@ CREATE FUNCTION dept(text) RETURNS dept
where the <replaceable>operator</replaceable> token follows the syntax
rules of <xref linkend="sql-syntax-operators">, or is one of the
key words <token>AND</token>, <token>OR</token>, and
<token>NOT</token>, or is a qualified operator name
<token>NOT</token>, or is a qualified operator name in the form
<synopsis>
<literal>OPERATOR(</><replaceable>schema</><literal>.</><replaceable>operatorname</><literal>)</>
</synopsis>
@ -1078,7 +1152,7 @@ sqrt(2)
</synopsis>
where <replaceable>aggregate_name</replaceable> is a previously
defined aggregate (possibly a qualified name), and
defined aggregate (possibly qualified with a schema name), and
<replaceable>expression</replaceable> is
any value expression that does not itself contain an aggregate
expression.