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Arrange for an explicit cast applied to an ARRAY[] constructor to be applied

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directly to all the member expressions, instead of the previous implementation
where the ARRAY[] constructor would infer a common element type and then we'd
coerce the finished array after the fact.  This has a number of benefits,
one being that we can allow an empty ARRAY[] construct so long as its
element type is specified by such a cast.

Brendan Jurd, minor fixes by me.
This commit is contained in:
Tom Lane
2008-03-20 21:42:48 +00:00
parent 8759b79d0f
commit 6b0706ac33
11 changed files with 312 additions and 100 deletions
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42
doc/src/sgml/syntax.sgml
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@ -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>
@ -1553,6 +1568,19 @@ SELECT ARRAY[f1, f2, '{{9,10},{11,12}}'::int[]] FROM arr;
</programlisting>
</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