array_agg aggregate function, as per SQL:2008, but without ORDER BY clause
Rearrange the documentation a bit now that array_agg and xmlagg have similar semantics and issues. best of Robert Haas, Jeff Davis, Peter Eisentraut
This commit is contained in:
Peter Eisentraut
parent
69a0e2f76d
commit
3379fae6de
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@ -1,4 +1,4 @@
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<!-- $PostgreSQL: pgsql/doc/src/sgml/func.sgml,v 1.457 2008/11/12 13:09:27 petere Exp $ -->
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<!-- $PostgreSQL: pgsql/doc/src/sgml/func.sgml,v 1.458 2008/11/13 15:59:50 petere Exp $ -->
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<chapter id="functions">
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<title>Functions and Operators</title>
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@ -8353,7 +8353,7 @@ SELECT xmlroot(xmlparse(document '<?xml version="1.1"?><content>abc</content>'),
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</para>
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</sect3>
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<sect3>
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<sect3 id="functions-xml-xmlagg">
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<title><literal>xmlagg</literal></title>
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<indexterm>
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@ -8366,10 +8366,10 @@ SELECT xmlroot(xmlparse(document '<?xml version="1.1"?><content>abc</content>'),
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<para>
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The function <function>xmlagg</function> is, unlike the other
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functions below, an aggregate function. It concatenates the
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functions described here, an aggregate function. It concatenates the
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input values to the aggregate function call,
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like <function>xmlconcat</function> does.
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See <xref linkend="functions-aggregate"> for general information
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See <xref linkend="functions-aggregate"> for additional information
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about aggregate functions.
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</para>
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@ -8387,11 +8387,9 @@ SELECT xmlagg(x) FROM test;
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</para>
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<para>
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Note that in the current implementation, the order of the
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concatenation is in principle undefined. Making the input values
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to be sorted in some other way will usually work, however. For
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instance, in the above example, one could influence the order
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like so:
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The influence the order of the concatenation, something like the
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following approach to sort the input values can be used:
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<screen><![CDATA[
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SELECT xmlagg(x) FROM (SELECT * FROM test ORDER BY y DESC) AS tab;
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xmlagg
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@ -8399,11 +8397,8 @@ SELECT xmlagg(x) FROM (SELECT * FROM test ORDER BY y DESC) AS tab;
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<bar/><foo>abc</foo>
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]]></screen>
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But this approach is not guaranteed to work in all situations and
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in all versions of PostgreSQL. A future version of PostgreSQL
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will probably provide an additional feature to control the order
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in a proper way (<literal>xmlagg(expr ORDER BY expr, expr,
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...</literal>).
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Again, see <xref linkend="functions-aggregate"> for additional
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information.
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</para>
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</sect3>
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@ -9490,6 +9485,11 @@ SELECT NULLIF(value, '(none)') ...
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</tbody>
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</tgroup>
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</table>
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<para>
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See also <xref linkend="functions-aggregate"> about the aggregate
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function <function>array_agg</function> for use with arrays.
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</para>
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</sect1>
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<sect1 id="functions-aggregate">
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@ -9526,6 +9526,22 @@ SELECT NULLIF(value, '(none)') ...
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</thead>
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<tbody>
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<row>
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<entry>
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<indexterm>
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<primary>array_agg</primary>
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</indexterm>
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<function>array_agg(<replaceable class="parameter">expression</replaceable>)</function>
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</entry>
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<entry>
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any
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</entry>
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<entry>
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array of the argument type
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</entry>
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<entry>input values concatenated into an array</entry>
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</row>
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<row>
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<entry>
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<indexterm>
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@ -9684,6 +9700,22 @@ SELECT NULLIF(value, '(none)') ...
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</entry>
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<entry>sum of <replaceable class="parameter">expression</replaceable> across all input values</entry>
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</row>
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<row>
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<entry>
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<indexterm>
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<primary>xmlagg</primary>
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</indexterm>
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<function>xmlagg(<replaceable class="parameter">expression</replaceable>)</function>
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</entry>
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<entry>
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<type>xml</type>
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</entry>
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<entry>
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<type>xml</type>
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</entry>
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<entry>concatenation of XML values (see also <xref linkend="functions-xml-xmlagg">)</entry>
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</row>
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</tbody>
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</tgroup>
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</table>
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@ -9692,8 +9724,10 @@ SELECT NULLIF(value, '(none)') ...
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It should be noted that except for <function>count</function>,
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these functions return a null value when no rows are selected. In
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particular, <function>sum</function> of no rows returns null, not
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zero as one might expect. The <function>coalesce</function> function can be
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used to substitute zero for null when necessary.
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zero as one might expect, and <function>array_agg</function>
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returns null rather than an empty array when there are no input
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rows. The <function>coalesce</function> function can be used to
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substitute zero or an empty array for null when necessary.
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</para>
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<note>
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@ -9733,6 +9767,25 @@ SELECT count(*) FROM sometable;
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</para>
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</note>
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<para>
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The aggregate functions <function>array_agg</function>
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and <function>xmlagg</function>, as well as similar user-defined
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aggregate functions, produce meaningfully different result values
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depending on the order of the input values. In the current
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implementation, the order of the concatenation is in principle
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undefined. Making the input values to be sorted in some other way
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will usually work, however. For example:
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<screen><![CDATA[
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SELECT xmlagg(x) FROM (SELECT * FROM test ORDER BY y DESC) AS tab;
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]]></screen>
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But this approach is not guaranteed to work in all situations, and
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it is not strictly SQL-conforming. A future version of PostgreSQL
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might provide an additional feature to control the order in a
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better-defined way (<literal>xmlagg(expr ORDER BY expr, expr,
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...</literal>).
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</para>
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<para>
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<xref linkend="functions-aggregate-statistics-table"> shows
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@ -350,7 +350,7 @@ S094 Arrays of reference types NO
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S095 Array constructors by query YES
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S096 Optional array bounds YES
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S097 Array element assignment NO
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S098 ARRAY_AGG NO
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S098 ARRAY_AGG NO ORDER BY clause not supported
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S111 ONLY in query expressions YES
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S151 Type predicate NO
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S161 Subtype treatment NO
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@ -6,12 +6,13 @@
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* Copyright (c) 2003-2008, PostgreSQL Global Development Group
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*
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* IDENTIFICATION
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* $PostgreSQL: pgsql/src/backend/utils/adt/array_userfuncs.c,v 1.23 2008/01/01 19:45:52 momjian Exp $
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* $PostgreSQL: pgsql/src/backend/utils/adt/array_userfuncs.c,v 1.24 2008/11/13 15:59:50 petere Exp $
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*
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*-------------------------------------------------------------------------
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*/
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#include "postgres.h"
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#include "nodes/execnodes.h"
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#include "utils/array.h"
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#include "utils/builtins.h"
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#include "utils/lsyscache.h"
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@ -465,3 +466,34 @@ create_singleton_array(FunctionCallInfo fcinfo,
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return construct_md_array(dvalues, NULL, ndims, dims, lbs, element_type,
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typlen, typbyval, typalign);
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}
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Datum
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array_agg_transfn(PG_FUNCTION_ARGS)
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{
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Oid arg1_typeid = get_fn_expr_argtype(fcinfo->flinfo, 1);
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if (arg1_typeid == InvalidOid)
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ereport(ERROR, (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
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errmsg("could not determine input data type")));
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/* cannot be called directly because of internal-type argument */
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Assert(fcinfo->context && IsA(fcinfo->context, AggState));
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PG_RETURN_POINTER(accumArrayResult(PG_ARGISNULL(0) ? NULL : (ArrayBuildState *) PG_GETARG_POINTER(0),
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PG_ARGISNULL(1) ? (Datum) 0 : PG_GETARG_DATUM(1),
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PG_ARGISNULL(1),
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arg1_typeid,
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((AggState *) fcinfo->context)->aggcontext));
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}
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Datum
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array_agg_finalfn(PG_FUNCTION_ARGS)
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{
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/* cannot be called directly because of internal-type argument */
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Assert(fcinfo->context && IsA(fcinfo->context, AggState));
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if (PG_ARGISNULL(0))
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PG_RETURN_NULL(); /* returns null iff no input values */
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PG_RETURN_ARRAYTYPE_P(makeArrayResult((ArrayBuildState *) PG_GETARG_POINTER(0), CurrentMemoryContext));
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}
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@ -37,7 +37,7 @@
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* Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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* $PostgreSQL: pgsql/src/include/catalog/catversion.h,v 1.504 2008/11/12 13:09:27 petere Exp $
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* $PostgreSQL: pgsql/src/include/catalog/catversion.h,v 1.505 2008/11/13 15:59:50 petere Exp $
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*
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*-------------------------------------------------------------------------
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*/
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@ -53,6 +53,6 @@
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*/
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/* yyyymmddN */
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#define CATALOG_VERSION_NO 200811121
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#define CATALOG_VERSION_NO 200811131
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#endif
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@ -8,7 +8,7 @@
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* Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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* $PostgreSQL: pgsql/src/include/catalog/pg_aggregate.h,v 1.66 2008/03/27 03:57:34 tgl Exp $
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* $PostgreSQL: pgsql/src/include/catalog/pg_aggregate.h,v 1.67 2008/11/13 15:59:50 petere Exp $
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*
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* NOTES
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* the genbki.sh script reads this file and generates .bki
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@ -220,6 +220,9 @@ DATA(insert ( 2243 bitor - 0 1560 _null_ ));
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/* xml */
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DATA(insert ( 2901 xmlconcat2 - 0 142 _null_ ));
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/* array */
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DATA(insert ( 2335 array_agg_transfn array_agg_finalfn 0 2281 _null_ ));
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/*
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* prototypes for functions in pg_aggregate.c
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*/
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@ -7,7 +7,7 @@
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* Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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* $PostgreSQL: pgsql/src/include/catalog/pg_proc.h,v 1.526 2008/11/12 13:38:04 tgl Exp $
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* $PostgreSQL: pgsql/src/include/catalog/pg_proc.h,v 1.527 2008/11/13 15:59:50 petere Exp $
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*
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* NOTES
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* The script catalog/genbki.sh reads this file and generates .bki
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@ -1022,6 +1022,13 @@ DATA(insert OID = 1193 ( array_fill PGNSP PGUID 12 1 0 0 f f f f i 2 2277 "2283
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DESCR("array constructor with value");
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DATA(insert OID = 1286 ( array_fill PGNSP PGUID 12 1 0 0 f f f f i 3 2277 "2283 1007 1007" _null_ _null_ _null_ array_fill_with_lower_bounds _null_ _null_ _null_ ));
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DESCR("array constructor with value");
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DATA(insert OID = 2333 ( array_agg_transfn PGNSP PGUID 12 1 0 0 f f f f i 2 2281 "2281 2283" _null_ _null_ _null_ array_agg_transfn _null_ _null_ _null_ ));
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DESCR("array_agg transition function");
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DATA(insert OID = 2334 ( array_agg_finalfn PGNSP PGUID 12 1 0 0 f f f f i 1 2277 "2281" _null_ _null_ _null_ array_agg_finalfn _null_ _null_ _null_ ));
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DESCR("array_agg final function");
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DATA(insert OID = 2335 ( array_agg PGNSP PGUID 12 1 0 0 t f f f i 1 2277 "2283" _null_ _null_ _null_ aggregate_dummy _null_ _null_ _null_ ));
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DESCR("concatenate aggregate input into an array");
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DATA(insert OID = 760 ( smgrin PGNSP PGUID 12 1 0 0 f f t f s 1 210 "2275" _null_ _null_ _null_ smgrin _null_ _null_ _null_ ));
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DESCR("I/O");
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DATA(insert OID = 761 ( smgrout PGNSP PGUID 12 1 0 0 f f t f s 1 2275 "210" _null_ _null_ _null_ smgrout _null_ _null_ _null_ ));
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@ -49,7 +49,7 @@
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* Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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* $PostgreSQL: pgsql/src/include/utils/array.h,v 1.70 2008/11/12 13:09:28 petere Exp $
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* $PostgreSQL: pgsql/src/include/utils/array.h,v 1.71 2008/11/13 15:59:50 petere Exp $
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*
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*-------------------------------------------------------------------------
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*/
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@ -275,4 +275,7 @@ extern ArrayType *create_singleton_array(FunctionCallInfo fcinfo,
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Datum element,
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int ndims);
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extern Datum array_agg_transfn(PG_FUNCTION_ARGS);
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extern Datum array_agg_finalfn(PG_FUNCTION_ARGS);
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#endif /* ARRAY_H */
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@ -1125,3 +1125,39 @@ select c, cardinality(c), d, cardinality(d) from arrtest;
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{foo,new_word} | 2 | {bar,foo} | 2
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(3 rows)
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select array_agg(unique1) from tenk1 where unique1 < 15;
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array_agg
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--------------------------------------
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{4,2,1,6,14,9,8,5,3,13,12,11,7,10,0}
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(1 row)
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select array_agg(ten) from tenk1 where unique1 < 15;
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array_agg
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---------------------------------
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{4,2,1,6,4,9,8,5,3,3,2,1,7,0,0}
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(1 row)
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select array_agg(nullif(ten, 4)) from tenk1 where unique1 < 15;
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array_agg
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---------------------------------------
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{NULL,2,1,6,NULL,9,8,5,3,3,2,1,7,0,0}
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(1 row)
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select cardinality(array_agg(unique1)) from tenk1 where unique1 < 15;
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cardinality
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-------------
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15
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(1 row)
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select array_agg(unique1) from (select * from tenk1 order by unique1 asc) as tab where unique1 < 15;
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array_agg
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--------------------------------------
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{0,1,2,3,4,5,6,7,8,9,10,11,12,13,14}
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(1 row)
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select array_agg(unique1) from tenk1 where unique1 < -15;
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array_agg
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-----------
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(1 row)
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@ -395,3 +395,10 @@ select array_length(array[[1,2,3], [4,5,6]], 3);
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select cardinality(array[1,2,3]);
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select cardinality(array[[1,2,3], [4,5,6]]);
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select c, cardinality(c), d, cardinality(d) from arrtest;
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select array_agg(unique1) from tenk1 where unique1 < 15;
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select array_agg(ten) from tenk1 where unique1 < 15;
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select array_agg(nullif(ten, 4)) from tenk1 where unique1 < 15;
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select cardinality(array_agg(unique1)) from tenk1 where unique1 < 15;
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select array_agg(unique1) from (select * from tenk1 order by unique1 asc) as tab where unique1 < 15;
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select array_agg(unique1) from tenk1 where unique1 < -15;
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