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Allow aggregate functions to be VARIADIC.

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There's no inherent reason why an aggregate function can't be variadic
(even VARIADIC ANY) if its transition function can handle the case.
Indeed, this patch to add the feature touches none of the planner or
executor, and little of the parser; the main missing stuff was DDL and
pg_dump support.

It is true that variadic aggregates can create the same sort of ambiguity
about parameters versus ORDER BY keys that was complained of when we
(briefly) had both one- and two-argument forms of string_agg().  However,
the policy formed in response to that discussion only said that we'd not
create any built-in aggregates with varying numbers of arguments, not that
we shouldn't allow users to do it.  So the logical extension of that is
we can allow users to make variadic aggregates as long as we're wary about
shipping any such in core.

In passing, this patch allows aggregate function arguments to be named, to
the extent of remembering the names in pg_proc and dumping them in pg_dump.
You can't yet call an aggregate using named-parameter notation.  That seems
like a likely future extension, but it'll take some work, and it's not what
this patch is really about.  Likewise, there's still some work needed to
make window functions handle VARIADIC fully, but I left that for another
day.

initdb forced because of new aggvariadic field in Aggref parse nodes.
This commit is contained in:
Tom Lane
2013-09-03 17:08:38 -04:00
parent 8b290f3115
commit 0d3f4406df
35 changed files with 448 additions and 116 deletions
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36
doc/src/sgml/ref/create_aggregate.sgml
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@@ -21,7 +21,7 @@ PostgreSQL documentation
<refsynopsisdiv>
<synopsis>
CREATE AGGREGATE <replaceable class="PARAMETER">name</replaceable> ( <replaceable class="PARAMETER">input_data_type</replaceable> [ , ... ] ) (
CREATE AGGREGATE <replaceable class="parameter">name</replaceable> ( [ <replaceable class="parameter">argmode</replaceable> ] [ <replaceable class="parameter">arg_name</replaceable> ] <replaceable class="parameter">arg_data_type</replaceable> [ , ... ] ) (
SFUNC = <replaceable class="PARAMETER">sfunc</replaceable>,
STYPE = <replaceable class="PARAMETER">state_data_type</replaceable>
[ , FINALFUNC = <replaceable class="PARAMETER">ffunc</replaceable> ]
@@ -118,7 +118,7 @@ CREATE AGGREGATE <replaceable class="PARAMETER">name</replaceable> (
Note that this behavior is only available when
<replaceable class="PARAMETER">state_data_type</replaceable>
is the same as the first
<replaceable class="PARAMETER">input_data_type</replaceable>.
<replaceable class="PARAMETER">arg_data_type</replaceable>.
When these types are different, you must supply a nonnull initial
condition or use a nonstrict transition function.
</para>
@@ -187,12 +187,36 @@ SELECT col FROM tab ORDER BY col USING sortop LIMIT 1;
</varlistentry>
<varlistentry>
<term><replaceable class="PARAMETER">input_data_type</replaceable></term>
<term><replaceable class="parameter">argmode</replaceable></term>
<listitem>
<para>
The mode of an argument: <literal>IN</> or <literal>VARIADIC</>.
(Aggregate functions do not support <literal>OUT</> arguments.)
If omitted, the default is <literal>IN</>. Only the last argument
can be marked <literal>VARIADIC</>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><replaceable class="parameter">arg_name</replaceable></term>
<listitem>
<para>
The name of an argument. This is currently only useful for
documentation purposes. If omitted, the argument has no name.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><replaceable class="PARAMETER">arg_data_type</replaceable></term>
<listitem>
<para>
An input data type on which this aggregate function operates.
To create a zero-argument aggregate function, write <literal>*</>
in place of the list of input data types. (An example of such an
in place of the list of argument specifications. (An example of such an
aggregate is <function>count(*)</function>.)
</para>
</listitem>
@@ -205,8 +229,8 @@ SELECT col FROM tab ORDER BY col USING sortop LIMIT 1;
In the old syntax for <command>CREATE AGGREGATE</>, the input data type
is specified by a <literal>basetype</> parameter rather than being
written next to the aggregate name. Note that this syntax allows
only one input parameter. To define a zero-argument aggregate function,
specify the <literal>basetype</> as
only one input parameter. To define a zero-argument aggregate function
with this syntax, specify the <literal>basetype</> as
<literal>"ANY"</> (not <literal>*</>).
</para>
</listitem>