diff options
| -rw-r--r-- | doc/src/sgml/syntax.sgml | 41 |
1 files changed, 30 insertions, 11 deletions
diff --git a/doc/src/sgml/syntax.sgml b/doc/src/sgml/syntax.sgml index b4c4b5e23ef..48223943000 100644 --- a/doc/src/sgml/syntax.sgml +++ b/doc/src/sgml/syntax.sgml @@ -1259,6 +1259,12 @@ SELECT 3 OPERATOR(pg_catalog.+) 4; <listitem> <para> + A collation expression + </para> + </listitem> + + <listitem> + <para> A scalar subquery </para> </listitem> @@ -1898,8 +1904,8 @@ CAST ( <replaceable>expression</replaceable> AS <replaceable>type</replaceable> </note> </sect2> - <sect2 id="sql-syntax-collate-clause"> - <title>COLLATE Clause</title> + <sect2 id="sql-syntax-collate-exprs"> + <title>Collation Expressions</title> <indexterm> <primary>COLLATE</primary> @@ -1925,7 +1931,7 @@ CAST ( <replaceable>expression</replaceable> AS <replaceable>type</replaceable> </para> <para> - The two typical uses of the <literal>COLLATE</literal> clause are + The two common uses of the <literal>COLLATE</literal> clause are overriding the sort order in an <literal>ORDER BY</> clause, for example: <programlisting> @@ -1934,15 +1940,28 @@ SELECT a, b, c FROM tbl WHERE ... ORDER BY a COLLATE "C"; and overriding the collation of a function or operator call that has locale-sensitive results, for example: <programlisting> -SELECT * FROM tbl WHERE a > 'foo' COLLATE "C"; +SELECT * FROM tbl WHERE a > 'foo' COLLATE "C"; +</programlisting> + Note that in the latter case the <literal>COLLATE</> clause is + attached to an input argument of the operator we wish to affect. + It doesn't matter which argument of the operator or function call the + <literal>COLLATE</> clause is attached to, because the collation that is + applied by the operator or function is derived by considering all + arguments, and an explicit <literal>COLLATE</> clause will override the + collations of all other arguments. (Attaching non-matching + <literal>COLLATE</> clauses to more than one argument, however, is an + error. For more details see <xref linkend="collation">.) + Thus, this gives the same result as the previous example: +<programlisting> +SELECT * FROM tbl WHERE a COLLATE "C" > 'foo'; +</programlisting> + But this is an error: +<programlisting> +SELECT * FROM tbl WHERE (a > 'foo') COLLATE "C"; </programlisting> - In the latter case it doesn't matter which argument of the - operator of function call the <literal>COLLATE</> clause is - attached to, because the collation that is applied by the operator - or function is derived from all arguments, and - the <literal>COLLATE</> clause will override the collations of all - other arguments. Attaching nonmatching <literal>COLLATE</> - clauses to more than one argument, however, is an error. + because it attempts to apply a collation to the result of the + <literal>></> operator, which is of the non-collatable data type + <type>boolean</>. </para> </sect2> |