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Add support for an optional INTO clause to PL/PgSQL's EXECUTE command.

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This allows the result of executing a SELECT to be assigned to a row
variable, record variable, or list of scalars. Docs and regression tests
updated. Per Pavel Stehule, improvements and cleanup by Neil Conway.
This commit is contained in:
Neil Conway
2005-06-07 02:47:23 +00:00
parent 0f011f6daa
commit c59887f916
6 changed files with 169 additions and 25 deletions
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45
doc/src/sgml/plpgsql.sgml
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@ -1,5 +1,5 @@
<!--
$PostgreSQL: pgsql/doc/src/sgml/plpgsql.sgml,v 1.69 2005/05/26 04:08:31 momjian Exp $
$PostgreSQL: pgsql/doc/src/sgml/plpgsql.sgml,v 1.70 2005/06/07 02:47:15 neilc Exp $
-->
<chapter id="plpgsql">
@ -1251,13 +1251,14 @@ NULL;
<command>EXECUTE</command> statement is provided:
<synopsis>
EXECUTE <replaceable class="command">command-string</replaceable>;
EXECUTE <replaceable class="command">command-string</replaceable> [ INTO <replaceable>target</replaceable> ];
</synopsis>
where <replaceable>command-string</replaceable> is an expression
yielding a string (of type
<type>text</type>) containing the command
to be executed. This string is fed literally to the SQL engine.
yielding a string (of type <type>text</type>) containing the
command to be executed and <replaceable>target</replaceable> is a
record variable, row variable, or a comma-separated list of
simple variables and record/row fields.
</para>
<para>
@ -1276,16 +1277,22 @@ EXECUTE <replaceable class="command">command-string</replaceable>;
</para>
<para>
The results from <command>SELECT</command> commands are discarded
by <command>EXECUTE</command>, and <command>SELECT INTO</command>
is not currently supported within <command>EXECUTE</command>.
So there is no way to extract a result from a dynamically-created
<command>SELECT</command> using the plain <command>EXECUTE</command>
command. There are two other ways to do it, however: one is to use the
<command>FOR-IN-EXECUTE</>
loop form described in <xref linkend="plpgsql-records-iterating">,
and the other is to use a cursor with <command>OPEN-FOR-EXECUTE</>, as
described in <xref linkend="plpgsql-cursor-opening">.
The <literal>INTO</literal> clause specifies where the results of
a <command>SELECT</command> command should be assigned. If a row
or variable list is provided, it must exactly match the structure
of the results produced by the <command>SELECT</command> (when a
record variable is used, it will configure itself to match the
result's structure automatically). If multiple rows are returned,
only the first will be assigned to the <literal>INTO</literal>
variable. If no rows are returned, NULL is assigned to the
<literal>INTO</literal> variable. If no <literal>INTO</literal>
clause is specified, the results of a <command>SELECT</command>
command are discarded.
</para>
<para>
<command>SELECT INTO</command> is not currently supported within
<command>EXECUTE</command>.
</para>
<para>
@ -1364,7 +1371,7 @@ EXECUTE 'UPDATE tbl SET '
command, which has the form:
<synopsis>
GET DIAGNOSTICS <replaceable>variable</replaceable> = <replaceable>item</replaceable> <optional> , ... </optional> ;
GET DIAGNOSTICS <replaceable>variable</replaceable> = <replaceable>item</replaceable> <optional> , ... </optional>;
</synopsis>
This command allows retrieval of system status indicators. Each
@ -2173,7 +2180,7 @@ SELECT merge_db (1, 'dennis');
Another way is to use the cursor declaration syntax,
which in general is:
<synopsis>
<replaceable>name</replaceable> CURSOR <optional> ( <replaceable>arguments</replaceable> ) </optional> FOR <replaceable>query</replaceable> ;
<replaceable>name</replaceable> CURSOR <optional> ( <replaceable>arguments</replaceable> ) </optional> FOR <replaceable>query</replaceable>;
</synopsis>
(<literal>FOR</> may be replaced by <literal>IS</> for
<productname>Oracle</productname> compatibility.)
@ -2218,7 +2225,7 @@ DECLARE
<title><command>OPEN FOR</command> <replaceable>query</replaceable></title>
<synopsis>
OPEN <replaceable>unbound_cursor</replaceable> FOR <replaceable>query</replaceable> ;
OPEN <replaceable>unbound_cursor</replaceable> FOR <replaceable>query</replaceable>;
</synopsis>
<para>
@ -3188,7 +3195,7 @@ DECLARE
func_body text;
func_cmd text;
BEGIN
func_body := 'BEGIN' ;
func_body := 'BEGIN';
-- Notice how we scan through the results of a query in a FOR loop
-- using the FOR &lt;record&gt; construct.