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Add aggsortop column to pg_aggregate, so that MIN/MAX optimization can

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be supported for all datatypes.  Add CREATE AGGREGATE and pg_dump support
too.  Add specialized min/max aggregates for bpchar, instead of depending
on text's min/max, because otherwise the possible use of bpchar indexes
cannot be recognized.
initdb forced because of catalog changes.
This commit is contained in:
Tom Lane
2005-04-12 04:26:34 +00:00
parent 3803f24379
commit 2e7a68896b
15 changed files with 356 additions and 123 deletions
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12
doc/src/sgml/catalogs.sgml
View File

@ -1,6 +1,6 @@
<!--
Documentation of the system catalogs, directed toward PostgreSQL developers
$PostgreSQL: pgsql/doc/src/sgml/catalogs.sgml,v 2.99 2005/03/29 19:44:22 tgl Exp $
$PostgreSQL: pgsql/doc/src/sgml/catalogs.sgml,v 2.100 2005/04/12 04:26:13 tgl Exp $
-->
<chapter id="catalogs">
@ -250,11 +250,17 @@
<entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
<entry>Final function (zero if none)</entry>
</row>
<row>
<entry><structfield>aggsortop</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal><link linkend="catalog-pg-operator"><structname>pg_operator</structname></link>.oid</literal></entry>
<entry>Associated sort operator (zero if none)</entry>
</row>
<row>
<entry><structfield>aggtranstype</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal><link linkend="catalog-pg-type"><structname>pg_type</structname></link>.oid</literal></entry>
<entry>The type of the aggregate function's internal transition (state) data</entry>
<entry>Data type of the aggregate function's internal transition (state) data</entry>
</row>
<row>
<entry><structfield>agginitval</structfield></entry>
@ -263,7 +269,7 @@
<entry>
The initial value of the transition state. This is a text
field containing the initial value in its external string
representation. If the value is null, the transition state
representation. If this field is null, the transition state
value starts out null.
</entry>
</row>

39
doc/src/sgml/ref/create_aggregate.sgml
View File

@ -1,5 +1,5 @@
<!--
$PostgreSQL: pgsql/doc/src/sgml/ref/create_aggregate.sgml,v 1.31 2005/01/04 00:39:53 tgl Exp $
$PostgreSQL: pgsql/doc/src/sgml/ref/create_aggregate.sgml,v 1.32 2005/04/12 04:26:15 tgl Exp $
PostgreSQL documentation
-->
@ -26,6 +26,7 @@ CREATE AGGREGATE <replaceable class="PARAMETER">name</replaceable> (
STYPE = <replaceable class="PARAMETER">state_data_type</replaceable>
[ , FINALFUNC = <replaceable class="PARAMETER">ffunc</replaceable> ]
[ , INITCOND = <replaceable class="PARAMETER">initial_condition</replaceable> ]
[ , SORTOP = <replaceable class="PARAMETER">sort_operator</replaceable> ]
)
</synopsis>
</refsynopsisdiv>
@ -125,6 +126,29 @@ CREATE AGGREGATE <replaceable class="PARAMETER">name</replaceable> (
<function>avg</function> returns null when it sees there were zero
input rows.
</para>
<para>
Aggregates that behave like <function>MIN</> or <function>MAX</> can
sometimes be optimized by looking into an index instead of scanning every
input row. If this aggregate can be so optimized, indicate it by
specifying a <firstterm>sort operator</>. The basic requirement is that
the aggregate must yield the first element in the sort ordering induced by
the operator; in other words
<programlisting>
SELECT agg(col) FROM tab;
</programlisting>
must be equivalent to
<programlisting>
SELECT col FROM tab ORDER BY col USING sortop LIMIT 1;
</programlisting>
Further assumptions are that the aggregate ignores null inputs, and that
it delivers a null result if and only if there were no non-null inputs.
Ordinarily, a datatype's <literal>&lt;</> operator is the proper sort
operator for <function>MIN</>, and <literal>&gt;</> is the proper sort
operator for <function>MAX</>. Note that the optimization will never
actually take effect unless the specified operator is the LessThan or
GreaterThan strategy member of a btree index opclass.
</para>
</refsect1>
<refsect1>
@ -211,6 +235,19 @@ CREATE AGGREGATE <replaceable class="PARAMETER">name</replaceable> (
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><replaceable class="PARAMETER">sort_operator</replaceable></term>
<listitem>
<para>
The associated sort operator for a <function>MIN</>- or
<function>MAX</>-like aggregate.
This is just an operator name (possibly schema-qualified).
The operator is assumed to have the same input datatypes as
the aggregate.
</para>
</listitem>
</varlistentry>
</variablelist>
<para>