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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
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9 files changed

+164
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‎doc/src/sgml/func.sgml

Lines changed: 69 additions & 16 deletions
Original file line numberDiff line numberDiff line change
@@ -1,4 +1,4 @@
1-
<!-- $PostgreSQL: pgsql/doc/src/sgml/func.sgml,v 1.457 2008/11/12 13:09:27 petere Exp $ -->
1+
<!-- $PostgreSQL: pgsql/doc/src/sgml/func.sgml,v 1.458 2008/11/13 15:59:50 petere Exp $ -->
22

33
<chapter id="functions">
44
<title>Functions and Operators</title>
@@ -8353,7 +8353,7 @@ SELECT xmlroot(xmlparse(document '<?xml version="1.1"?><content>abc</content>'),
83538353
</para>
83548354
</sect3>
83558355

8356-
<sect3>
8356+
<sect3 id="functions-xml-xmlagg">
83578357
<title><literal>xmlagg</literal></title>
83588358

83598359
<indexterm>
@@ -8366,10 +8366,10 @@ SELECT xmlroot(xmlparse(document '<?xml version="1.1"?><content>abc</content>'),
83668366

83678367
<para>
83688368
The function <function>xmlagg</function> is, unlike the other
8369-
functions below, an aggregate function. It concatenates the
8369+
functions described here, an aggregate function. It concatenates the
83708370
input values to the aggregate function call,
83718371
like <function>xmlconcat</function> does.
8372-
See <xref linkend="functions-aggregate"> for general information
8372+
See <xref linkend="functions-aggregate"> for additional information
83738373
about aggregate functions.
83748374
</para>
83758375

@@ -8387,23 +8387,18 @@ SELECT xmlagg(x) FROM test;
83878387
</para>
83888388

83898389
<para>
8390-
Note that in the current implementation, the order of the
8391-
concatenation is in principle undefined. Making the input values
8392-
to be sorted in some other way will usually work, however. For
8393-
instance, in the above example, one could influence the order
8394-
like so:
8390+
The influence the order of the concatenation, something like the
8391+
following approach to sort the input values can be used:
8392+
83958393
<screen><![CDATA[
83968394
SELECT xmlagg(x) FROM (SELECT * FROM test ORDER BY y DESC) AS tab;
83978395
xmlagg
83988396
----------------------
83998397
<bar/><foo>abc</foo>
84008398
]]></screen>
84018399

8402-
But this approach is not guaranteed to work in all situations and
8403-
in all versions of PostgreSQL. A future version of PostgreSQL
8404-
will probably provide an additional feature to control the order
8405-
in a proper way (<literal>xmlagg(expr ORDER BY expr, expr,
8406-
...</literal>).
8400+
Again, see <xref linkend="functions-aggregate"> for additional
8401+
information.
84078402
</para>
84088403
</sect3>
84098404

@@ -9490,6 +9485,11 @@ SELECT NULLIF(value, '(none)') ...
94909485
</tbody>
94919486
</tgroup>
94929487
</table>
9488+
9489+
<para>
9490+
See also <xref linkend="functions-aggregate"> about the aggregate
9491+
function <function>array_agg</function> for use with arrays.
9492+
</para>
94939493
</sect1>
94949494

94959495
<sect1 id="functions-aggregate">
@@ -9526,6 +9526,22 @@ SELECT NULLIF(value, '(none)') ...
95269526
</thead>
95279527

95289528
<tbody>
9529+
<row>
9530+
<entry>
9531+
<indexterm>
9532+
<primary>array_agg</primary>
9533+
</indexterm>
9534+
<function>array_agg(<replaceable class="parameter">expression</replaceable>)</function>
9535+
</entry>
9536+
<entry>
9537+
any
9538+
</entry>
9539+
<entry>
9540+
array of the argument type
9541+
</entry>
9542+
<entry>input values concatenated into an array</entry>
9543+
</row>
9544+
95299545
<row>
95309546
<entry>
95319547
<indexterm>
@@ -9684,6 +9700,22 @@ SELECT NULLIF(value, '(none)') ...
96849700
</entry>
96859701
<entry>sum of <replaceable class="parameter">expression</replaceable> across all input values</entry>
96869702
</row>
9703+
9704+
<row>
9705+
<entry>
9706+
<indexterm>
9707+
<primary>xmlagg</primary>
9708+
</indexterm>
9709+
<function>xmlagg(<replaceable class="parameter">expression</replaceable>)</function>
9710+
</entry>
9711+
<entry>
9712+
<type>xml</type>
9713+
</entry>
9714+
<entry>
9715+
<type>xml</type>
9716+
</entry>
9717+
<entry>concatenation of XML values (see also <xref linkend="functions-xml-xmlagg">)</entry>
9718+
</row>
96879719
</tbody>
96889720
</tgroup>
96899721
</table>
@@ -9692,8 +9724,10 @@ SELECT NULLIF(value, '(none)') ...
96929724
It should be noted that except for <function>count</function>,
96939725
these functions return a null value when no rows are selected. In
96949726
particular, <function>sum</function> of no rows returns null, not
9695-
zero as one might expect. The <function>coalesce</function> function can be
9696-
used to substitute zero for null when necessary.
9727+
zero as one might expect, and <function>array_agg</function>
9728+
returns null rather than an empty array when there are no input
9729+
rows. The <function>coalesce</function> function can be used to
9730+
substitute zero or an empty array for null when necessary.
96979731
</para>
96989732

96999733
<note>
@@ -9733,6 +9767,25 @@ SELECT count(*) FROM sometable;
97339767
</para>
97349768
</note>
97359769

9770+
<para>
9771+
The aggregate functions <function>array_agg</function>
9772+
and <function>xmlagg</function>, as well as similar user-defined
9773+
aggregate functions, produce meaningfully different result values
9774+
depending on the order of the input values. In the current
9775+
implementation, the order of the concatenation is in principle
9776+
undefined. Making the input values to be sorted in some other way
9777+
will usually work, however. For example:
9778+
9779+
<screen><![CDATA[
9780+
SELECT xmlagg(x) FROM (SELECT * FROM test ORDER BY y DESC) AS tab;
9781+
]]></screen>
9782+
9783+
But this approach is not guaranteed to work in all situations, and
9784+
it is not strictly SQL-conforming. A future version of PostgreSQL
9785+
might provide an additional feature to control the order in a
9786+
better-defined way (<literal>xmlagg(expr ORDER BY expr, expr,
9787+
...</literal>).
9788+
</para>
97369789

97379790
<para>
97389791
<xref linkend="functions-aggregate-statistics-table"> shows

‎src/backend/catalog/sql_features.txt

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -350,7 +350,7 @@ S094 Arrays of reference types NO
350350
S095 Array constructors by query YES
351351
S096 Optional array bounds YES
352352
S097 Array element assignment NO
353-
S098 ARRAY_AGG NO
353+
S098 ARRAY_AGG NO ORDER BY clause not supported
354354
S111 ONLY in query expressions YES
355355
S151 Type predicate NO
356356
S161 Subtype treatment NO

‎src/backend/utils/adt/array_userfuncs.c

Lines changed: 33 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -6,12 +6,13 @@
66
* Copyright (c) 2003-2008, PostgreSQL Global Development Group
77
*
88
* IDENTIFICATION
9-
* $PostgreSQL: pgsql/src/backend/utils/adt/array_userfuncs.c,v 1.23 2008/01/01 19:45:52 momjian Exp $
9+
* $PostgreSQL: pgsql/src/backend/utils/adt/array_userfuncs.c,v 1.24 2008/11/13 15:59:50 petere Exp $
1010
*
1111
*-------------------------------------------------------------------------
1212
*/
1313
#include "postgres.h"
1414

15+
#include "nodes/execnodes.h"
1516
#include "utils/array.h"
1617
#include "utils/builtins.h"
1718
#include "utils/lsyscache.h"
@@ -465,3 +466,34 @@ create_singleton_array(FunctionCallInfo fcinfo,
465466
return construct_md_array(dvalues, NULL, ndims, dims, lbs, element_type,
466467
typlen, typbyval, typalign);
467468
}
469+
470+
Datum
471+
array_agg_transfn(PG_FUNCTION_ARGS)
472+
{
473+
Oid arg1_typeid = get_fn_expr_argtype(fcinfo->flinfo, 1);
474+
475+
if (arg1_typeid == InvalidOid)
476+
ereport(ERROR, (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
477+
errmsg("could not determine input data type")));
478+
479+
/* cannot be called directly because of internal-type argument */
480+
Assert(fcinfo->context && IsA(fcinfo->context, AggState));
481+
482+
PG_RETURN_POINTER(accumArrayResult(PG_ARGISNULL(0) ? NULL : (ArrayBuildState *) PG_GETARG_POINTER(0),
483+
PG_ARGISNULL(1) ? (Datum) 0 : PG_GETARG_DATUM(1),
484+
PG_ARGISNULL(1),
485+
arg1_typeid,
486+
((AggState *) fcinfo->context)->aggcontext));
487+
}
488+
489+
Datum
490+
array_agg_finalfn(PG_FUNCTION_ARGS)
491+
{
492+
/* cannot be called directly because of internal-type argument */
493+
Assert(fcinfo->context && IsA(fcinfo->context, AggState));
494+
495+
if (PG_ARGISNULL(0))
496+
PG_RETURN_NULL(); /* returns null iff no input values */
497+
498+
PG_RETURN_ARRAYTYPE_P(makeArrayResult((ArrayBuildState *) PG_GETARG_POINTER(0), CurrentMemoryContext));
499+
}

‎src/include/catalog/catversion.h

Lines changed: 2 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -37,7 +37,7 @@
3737
* Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
3838
* Portions Copyright (c) 1994, Regents of the University of California
3939
*
40-
* $PostgreSQL: pgsql/src/include/catalog/catversion.h,v 1.504 2008/11/12 13:09:27 petere Exp $
40+
* $PostgreSQL: pgsql/src/include/catalog/catversion.h,v 1.505 2008/11/13 15:59:50 petere Exp $
4141
*
4242
*-------------------------------------------------------------------------
4343
*/
@@ -53,6 +53,6 @@
5353
*/
5454

5555
/* yyyymmddN */
56-
#define CATALOG_VERSION_NO 200811121
56+
#define CATALOG_VERSION_NO 200811131
5757

5858
#endif

‎src/include/catalog/pg_aggregate.h

Lines changed: 4 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -8,7 +8,7 @@
88
* Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
99
* Portions Copyright (c) 1994, Regents of the University of California
1010
*
11-
* $PostgreSQL: pgsql/src/include/catalog/pg_aggregate.h,v 1.66 2008/03/27 03:57:34 tgl Exp $
11+
* $PostgreSQL: pgsql/src/include/catalog/pg_aggregate.h,v 1.67 2008/11/13 15:59:50 petere Exp $
1212
*
1313
* NOTES
1414
* the genbki.sh script reads this file and generates .bki
@@ -220,6 +220,9 @@ DATA(insert ( 2243 bitor - 0 1560 _null_ ));
220220
/* xml */
221221
DATA(insert ( 2901 xmlconcat2 - 0 142 _null_ ));
222222

223+
/* array */
224+
DATA(insert ( 2335 array_agg_transfn array_agg_finalfn 0 2281 _null_ ));
225+
223226
/*
224227
* prototypes for functions in pg_aggregate.c
225228
*/

‎src/include/catalog/pg_proc.h

Lines changed: 8 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -7,7 +7,7 @@
77
* Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
88
* Portions Copyright (c) 1994, Regents of the University of California
99
*
10-
* $PostgreSQL: pgsql/src/include/catalog/pg_proc.h,v 1.526 2008/11/12 13:38:04 tgl Exp $
10+
* $PostgreSQL: pgsql/src/include/catalog/pg_proc.h,v 1.527 2008/11/13 15:59:50 petere Exp $
1111
*
1212
* NOTES
1313
* The script catalog/genbki.sh reads this file and generates .bki
@@ -1022,6 +1022,13 @@ DATA(insert OID = 1193 ( array_fill PGNSP PGUID 12 1 0 0 f f f f i 2 2277 "2283
10221022
DESCR("array constructor with value");
10231023
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_ ));
10241024
DESCR("array constructor with value");
1025+
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_ ));
1026+
DESCR("array_agg transition function");
1027+
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_ ));
1028+
DESCR("array_agg final function");
1029+
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_ ));
1030+
DESCR("concatenate aggregate input into an array");
1031+
10251032
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_ ));
10261033
DESCR("I/O");
10271034
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_ ));

‎src/include/utils/array.h

Lines changed: 4 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -49,7 +49,7 @@
4949
* Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
5050
* Portions Copyright (c) 1994, Regents of the University of California
5151
*
52-
* $PostgreSQL: pgsql/src/include/utils/array.h,v 1.70 2008/11/12 13:09:28 petere Exp $
52+
* $PostgreSQL: pgsql/src/include/utils/array.h,v 1.71 2008/11/13 15:59:50 petere Exp $
5353
*
5454
*-------------------------------------------------------------------------
5555
*/
@@ -275,4 +275,7 @@ extern ArrayType *create_singleton_array(FunctionCallInfo fcinfo,
275275
Datum element,
276276
int ndims);
277277

278+
extern Datum array_agg_transfn(PG_FUNCTION_ARGS);
279+
extern Datum array_agg_finalfn(PG_FUNCTION_ARGS);
280+
278281
#endif /* ARRAY_H */

‎src/test/regress/expected/arrays.out

Lines changed: 36 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -1125,3 +1125,39 @@ select c, cardinality(c), d, cardinality(d) from arrtest;
11251125
{foo,new_word} | 2 | {bar,foo} | 2
11261126
(3 rows)
11271127

1128+
select array_agg(unique1) from tenk1 where unique1 < 15;
1129+
array_agg
1130+
--------------------------------------
1131+
{4,2,1,6,14,9,8,5,3,13,12,11,7,10,0}
1132+
(1 row)
1133+
1134+
select array_agg(ten) from tenk1 where unique1 < 15;
1135+
array_agg
1136+
---------------------------------
1137+
{4,2,1,6,4,9,8,5,3,3,2,1,7,0,0}
1138+
(1 row)
1139+
1140+
select array_agg(nullif(ten, 4)) from tenk1 where unique1 < 15;
1141+
array_agg
1142+
---------------------------------------
1143+
{NULL,2,1,6,NULL,9,8,5,3,3,2,1,7,0,0}
1144+
(1 row)
1145+
1146+
select cardinality(array_agg(unique1)) from tenk1 where unique1 < 15;
1147+
cardinality
1148+
-------------
1149+
15
1150+
(1 row)
1151+
1152+
select array_agg(unique1) from (select * from tenk1 order by unique1 asc) as tab where unique1 < 15;
1153+
array_agg
1154+
--------------------------------------
1155+
{0,1,2,3,4,5,6,7,8,9,10,11,12,13,14}
1156+
(1 row)
1157+
1158+
select array_agg(unique1) from tenk1 where unique1 < -15;
1159+
array_agg
1160+
-----------
1161+
1162+
(1 row)
1163+

‎src/test/regress/sql/arrays.sql

Lines changed: 7 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -395,3 +395,10 @@ select array_length(array[[1,2,3], [4,5,6]], 3);
395395
select cardinality(array[1,2,3]);
396396
select cardinality(array[[1,2,3], [4,5,6]]);
397397
select c, cardinality(c), d, cardinality(d) from arrtest;
398+
399+
select array_agg(unique1) from tenk1 where unique1 < 15;
400+
select array_agg(ten) from tenk1 where unique1 < 15;
401+
select array_agg(nullif(ten, 4)) from tenk1 where unique1 < 15;
402+
select cardinality(array_agg(unique1)) from tenk1 where unique1 < 15;
403+
select array_agg(unique1) from (select * from tenk1 order by unique1 asc) as tab where unique1 < 15;
404+
select array_agg(unique1) from tenk1 where unique1 < -15;

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