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Diffstat (limited to 'doc/src/sgml/syntax.sgml')
| -rw-r--r-- | doc/src/sgml/syntax.sgml | 42 |
1 files changed, 35 insertions, 7 deletions
diff --git a/doc/src/sgml/syntax.sgml b/doc/src/sgml/syntax.sgml index 8761b6e1da7..e677d80d5ce 100644 --- a/doc/src/sgml/syntax.sgml +++ b/doc/src/sgml/syntax.sgml @@ -1,4 +1,4 @@ -<!-- $PostgreSQL: pgsql/doc/src/sgml/syntax.sgml,v 1.121 2008/01/23 19:51:29 tgl Exp $ --> +<!-- $PostgreSQL: pgsql/doc/src/sgml/syntax.sgml,v 1.122 2008/03/20 21:42:47 tgl Exp $ --> <chapter id="sql-syntax"> <title>SQL Syntax</title> @@ -1305,7 +1305,7 @@ sqrt(2) where <replaceable>aggregate_name</replaceable> is a previously defined aggregate (possibly qualified with a schema name), and - <replaceable>expression</replaceable> is + <replaceable>expression</replaceable> is any value expression that does not itself contain an aggregate expression. </para> @@ -1335,7 +1335,7 @@ sqrt(2) <para> The predefined aggregate functions are described in <xref linkend="functions-aggregate">. Other aggregate functions can be added - by the user. + by the user. </para> <para> @@ -1495,9 +1495,9 @@ SELECT name, (SELECT max(pop) FROM cities WHERE cities.state = states.name) <para> An array constructor is an expression that builds an array value from values for its member elements. A simple array - constructor + constructor consists of the key word <literal>ARRAY</literal>, a left square bracket - <literal>[</>, one or more expressions (separated by commas) for the + <literal>[</>, a list of expressions (separated by commas) for the array element values, and finally a right square bracket <literal>]</>. For example: <programlisting> @@ -1507,9 +1507,22 @@ SELECT ARRAY[1,2,3+4]; {1,2,7} (1 row) </programlisting> - The array element type is the common type of the member expressions, + By default, + the array element type is the common type of the member expressions, determined using the same rules as for <literal>UNION</> or - <literal>CASE</> constructs (see <xref linkend="typeconv-union-case">). + <literal>CASE</> constructs (see <xref linkend="typeconv-union-case">). + You can override this by explicitly casting the array constructor to the + desired type, for example: +<programlisting> +SELECT ARRAY[1,2,22.7]::integer[]; + array +---------- + {1,2,23} +(1 row) +</programlisting> + This has the same effect as casting each expression to the array + element type individually. + For more on casting, see <xref linkend="sql-syntax-type-casts">. </para> <para> @@ -1534,6 +1547,8 @@ SELECT ARRAY[[1,2],[3,4]]; Since multidimensional arrays must be rectangular, inner constructors at the same level must produce sub-arrays of identical dimensions. + Any cast applied to the outer <literal>ARRAY</> constructor propagates + automatically to all the inner constructors. </para> <para> @@ -1554,6 +1569,19 @@ SELECT ARRAY[f1, f2, '{{9,10},{11,12}}'::int[]] FROM arr; </para> <para> + You can construct an empty array, but since it's impossible to have an + array with no type, you must explicitly cast your empty array to the + desired type. For example: +<programlisting> +SELECT ARRAY[]::integer[]; + array +------- + {} +(1 row) +</programlisting> + </para> + + <para> It is also possible to construct an array from the results of a subquery. In this form, the array constructor is written with the key word <literal>ARRAY</literal> followed by a parenthesized (not |