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plpgsql does OUT parameters, as per my proposal a few weeks ago.

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This commit is contained in:
Tom Lane
2005-04-05 06:22:17 +00:00
parent 2af664e7ce
commit fd97cf4df0
10 changed files with 959 additions and 360 deletions
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140
doc/src/sgml/plpgsql.sgml
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@@ -1,5 +1,5 @@
<!--
$PostgreSQL: pgsql/doc/src/sgml/plpgsql.sgml,v 1.62 2005/03/13 09:36:30 neilc Exp $
$PostgreSQL: pgsql/doc/src/sgml/plpgsql.sgml,v 1.63 2005/04/05 06:22:14 tgl Exp $
-->
<chapter id="plpgsql">
@@ -83,7 +83,7 @@ $PostgreSQL: pgsql/doc/src/sgml/plpgsql.sgml,v 1.62 2005/03/13 09:36:30 neilc Ex
that contains many statements for which execution plans might be
required will only prepare and save those plans that are really
used during the lifetime of the database connection. This can
substantially reduce the total amount of time required to parse,
substantially reduce the total amount of time required to parse
and generate execution plans for the statements in a
<application>PL/pgSQL</> function. A disadvantage is that errors
in a specific expression or command may not be detected until that
@@ -215,6 +215,7 @@ $$ LANGUAGE plpgsql;
<type>void</> if it has no useful return value.
</para>
<note>
<para>
<application>PL/pgSQL</> does not currently have full support for
domain types: it treats a domain the same as the underlying scalar
@@ -223,6 +224,20 @@ $$ LANGUAGE plpgsql;
it is a hazard if you declare a <application>PL/pgSQL</> function
as returning a domain type.
</para>
</note>
<para>
<application>PL/pgSQL</> functions can also be declared with output
parameters in place of an explicit specification of the return type.
This does not add any fundamental capability to the language, but
it is often convenient, especially for returning multiple values.
</para>
<para>
Specific examples appear in
<xref linkend="plpgsql-declaration-aliases"> and
<xref linkend="plpgsql-statements-returning">.
</para>
</sect2>
</sect1>
@@ -631,12 +646,12 @@ DECLARE
v_string ALIAS FOR $1;
index ALIAS FOR $2;
BEGIN
-- some computations here
-- some computations using v_string and index here
END;
$$ LANGUAGE plpgsql;
CREATE FUNCTION concat_selected_fields(in_t tablename) RETURNS text AS $$
CREATE FUNCTION concat_selected_fields(in_t sometablename) RETURNS text AS $$
BEGIN
RETURN in_t.f1 || in_t.f3 || in_t.f5 || in_t.f7;
END;
@@ -644,6 +659,49 @@ $$ LANGUAGE plpgsql;
</programlisting>
</para>
<para>
When a <application>PL/pgSQL</application> function is declared
with output parameters, the output parameters are given
<literal>$<replaceable>n</replaceable></literal> names and optional
aliases in just the same way as the normal input parameters. An
output parameter is effectively a variable that starts out NULL;
it should be assigned to during the execution of the function.
The final value of the parameter is what is returned. For instance,
the sales-tax example could also be done this way:
<programlisting>
CREATE FUNCTION sales_tax(subtotal real, OUT tax real) AS $$
BEGIN
tax := subtotal * 0.06;
RETURN;
END;
$$ LANGUAGE plpgsql;
</programlisting>
Notice that we omitted <literal>RETURNS real</> &mdash; we could have
included it, but it would be redundant.
</para>
<para>
Output parameters are most useful when returning multiple values.
A trivial example is:
<programlisting>
CREATE FUNCTION sum_n_product(x int, y int, OUT sum int, OUT prod int) AS $$
BEGIN
sum := x + y;
prod := x * y;
RETURN;
END;
$$ LANGUAGE plpgsql;
</programlisting>
As discussed in <xref linkend="xfunc-output-parameters">, this
effectively creates an anonymous record type for the function's
results. If a <literal>RETURNS</> clause is given, it must say
<literal>RETURNS record</>.
</para>
<para>
When the return type of a <application>PL/pgSQL</application>
function is declared as a polymorphic type (<type>anyelement</type>
@@ -658,6 +716,7 @@ $$ LANGUAGE plpgsql;
though that is not required. <literal>$0</literal> can also be
given an alias. For example, this function works on any data type
that has a <literal>+</> operator:
<programlisting>
CREATE FUNCTION add_three_values(v1 anyelement, v2 anyelement, v3 anyelement)
RETURNS anyelement AS $$
@@ -668,6 +727,24 @@ BEGIN
RETURN result;
END;
$$ LANGUAGE plpgsql;
</programlisting>
</para>
<para>
The same effect can be had by declaring one or more output parameters as
<type>anyelement</type> or <type>anyarray</type>. In this case the
special <literal>$0</literal> parameter is not used; the output
parameters themselves serve the same purpose. For example:
<programlisting>
CREATE FUNCTION add_three_values(v1 anyelement, v2 anyelement, v3 anyelement,
OUT sum anyelement)
AS $$
BEGIN
sum := v1 + v2 + v3;
RETURN;
END;
$$ LANGUAGE plpgsql;
</programlisting>
</para>
</sect2>
@@ -756,18 +833,21 @@ user_id users.user_id%TYPE;
</para>
<para>
Here is an example of using composite types:
Here is an example of using composite types. <structname>table1</>
and <structname>table2</> are existing tables having at least the
mentioned fields:
<programlisting>
CREATE FUNCTION merge_fields(t_row tablename) RETURNS text AS $$
CREATE FUNCTION merge_fields(t_row table1) RETURNS text AS $$
DECLARE
t2_row table2name%ROWTYPE;
t2_row table2%ROWTYPE;
BEGIN
SELECT * INTO t2_row FROM table2name WHERE ... ;
SELECT * INTO t2_row FROM table2 WHERE ... ;
RETURN t_row.f1 || t2_row.f3 || t_row.f5 || t2_row.f7;
END;
$$ LANGUAGE plpgsql;
SELECT merge_fields(t.*) FROM tablename t WHERE ... ;
SELECT merge_fields(t.*) FROM table1 t WHERE ... ;
</programlisting>
</para>
</sect2>
@@ -1411,6 +1491,12 @@ RETURN <replaceable>expression</replaceable>;
as the <replaceable>expression</replaceable>.
</para>
<para>
If you declared the function with output parameters, write just
<command>RETURN</command> with no expression. The current values
of the output parameter variables will be returned.
</para>
<para>
The return value of a function cannot be left undefined. If
control reaches the end of the top-level block of the function
@@ -1441,8 +1527,30 @@ RETURN NEXT <replaceable>expression</replaceable>;
commands, and then a final <command>RETURN</command> command
with no argument is used to indicate that the function has
finished executing. <command>RETURN NEXT</command> can be used
with both scalar and composite data types; in the latter case, an
entire <quote>table</quote> of results will be returned.
with both scalar and composite data types; with a composite result
type, an entire <quote>table</quote> of results will be returned.
</para>
<para>
<command>RETURN NEXT</command> does not actually return from the
function &mdash; it simply saves away the value of the expression.
Execution then continues with the next statement in
the <application>PL/pgSQL</> function. As successive
<command>RETURN NEXT</command> commands are executed, the result
set is built up. A final <command>RETURN</command>, which should
have no argument, causes control to exit the function.
</para>
<para>
If you declared the function with output parameters, write just
<command>RETURN NEXT</command> with no expression. The current values
of the output parameter variable(s) will be saved for eventual return.
Note that you must declare the function as returning
<literal>SETOF record</literal> when there are
multiple output parameters, or
<literal>SETOF <replaceable>sometype</></literal> when there is
just one output parameter of type <replaceable>sometype</>, in
order to create a set-returning function with output parameters.
</para>
<para>
@@ -1457,16 +1565,6 @@ SELECT * FROM some_func();
<literal>FROM</literal> clause.
</para>
<para>
<command>RETURN NEXT</command> does not actually return from the
function; it simply saves away the value of the expression.
Execution then continues with the next statement in
the <application>PL/pgSQL</> function. As successive
<command>RETURN NEXT</command> commands are executed, the result
set is built up. A final <command>RETURN</command>, which should
have no argument, causes control to exit the function.
</para>
<note>
<para>
The current implementation of <command>RETURN NEXT</command>