Add string_agg aggregate functions. The one argument version concatenates

the input values into a string. The two argument version also does the same
thing, but inserts delimiters between elements.

Original patch by Pavel Stehule, reviewed by David E. Wheeler and me.

doc/src/sgml/func.sgml

-<!-- $PostgreSQL: pgsql/doc/src/sgml/func.sgml,v 1.498 2010/01/25 20:55:32 tgl Exp $ -->
+<!-- $PostgreSQL: pgsql/doc/src/sgml/func.sgml,v 1.499 2010/02/01 03:14:43 itagaki Exp $ -->
 
  <chapter id="functions">
   <title>Functions and Operators</title>
@@ -1789,6 +1789,10 @@
     </tgroup>
    </table>
 
+   <para>
+   See also <xref linkend="functions-aggregate"> about the aggregate
+   function <function>string_agg</function>.
+   </para>
 
    <table id="conversion-names">
     <title>Built-in Conversions</title>
@@ -9836,6 +9840,25 @@ SELECT NULLIF(value, '(none)') ...
       </entry>
      </row>
 
+     <row>
+      <entry>
+       <indexterm>
+        <primary>string_agg</primary>
+       </indexterm>
+       <function>
+         string_agg(<replaceable class="parameter">expression</replaceable> 
+                    [, <replaceable class="parameter">delimiter</replaceable> ] )
+       </function>
+      </entry>
+      <entry>
+       <type>text</type>
+      </entry>
+      <entry>
+       <type>text</type>
+      </entry>
+      <entry>input values concatenated into a string, optionally with delimiters</entry>
+     </row>
+
      <row>
       <entry><function>sum(<replaceable class="parameter">expression</replaceable>)</function></entry>
       <entry>

src/backend/utils/adt/varlena.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/utils/adt/varlena.c,v 1.174 2010/01/25 20:55:32 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/utils/adt/varlena.c,v 1.175 2010/02/01 03:14:43 itagaki Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -21,6 +21,7 @@
 #include "libpq/md5.h"
 #include "libpq/pqformat.h"
 #include "miscadmin.h"
+#include "nodes/execnodes.h"
 #include "parser/scansup.h"
 #include "regex/regex.h"
 #include "utils/builtins.h"
@@ -73,6 +74,7 @@ static bytea *bytea_substring(Datum str,
 				int L,
 				bool length_not_specified);
 static bytea *bytea_overlay(bytea *t1, bytea *t2, int sp, int sl);
+static StringInfo makeStringAggState(fmNodePtr context);
 
 
 /*****************************************************************************
@@ -3315,3 +3317,105 @@ pg_column_size(PG_FUNCTION_ARGS)
 
 	PG_RETURN_INT32(result);
 }
+
+/*
+ * string_agg - Concatenates values and returns string.
+ *
+ * Syntax: string_agg(value text, delimiter text = '') RETURNS text
+ *
+ * Note: Any NULL values are ignored. The first-call delimiter isn't
+ * actually used at all, and on subsequent calls the delimiter precedes
+ * the associated value.
+ */
+static StringInfo
+makeStringAggState(fmNodePtr context)
+{
+	StringInfo		state;
+	MemoryContext	aggcontext;
+	MemoryContext	oldcontext;
+
+	if (context && IsA(context, AggState))
+		aggcontext = ((AggState *) context)->aggcontext;
+	else if (context && IsA(context, WindowAggState))
+		aggcontext = ((WindowAggState *) context)->wincontext;
+	else
+	{
+		/* cannot be called directly because of internal-type argument */
+		elog(ERROR, "string_agg_transfn called in non-aggregate context");
+		aggcontext = NULL;		/* keep compiler quiet */
+	}
+
+	/* Create state in aggregate context */
+	oldcontext = MemoryContextSwitchTo(aggcontext);
+	state = makeStringInfo();
+	MemoryContextSwitchTo(oldcontext);
+
+	return state;
+}
+
+Datum
+string_agg_transfn(PG_FUNCTION_ARGS)
+{
+	StringInfo		state;
+
+	state = PG_ARGISNULL(0) ? NULL : (StringInfo) PG_GETARG_POINTER(0);
+
+	/* Append the element unless not null. */
+	if (!PG_ARGISNULL(1))
+	{
+		if (state == NULL)
+			state = makeStringAggState(fcinfo->context);
+		appendStringInfoText(state, PG_GETARG_TEXT_PP(1));	/* value */
+	}
+
+	/*
+	 * The transition type for string_agg() is declared to be "internal", which
+	 * is a pass-by-value type the same size as a pointer.	
+	 */
+	PG_RETURN_POINTER(state);
+}
+
+Datum 
+string_agg_delim_transfn(PG_FUNCTION_ARGS)
+{
+	StringInfo		state;
+
+	state = PG_ARGISNULL(0) ? NULL : (StringInfo) PG_GETARG_POINTER(0);
+
+	/* Append the value unless not null. */
+	if (!PG_ARGISNULL(1))
+	{
+		if (state == NULL)
+			state = makeStringAggState(fcinfo->context);
+		else if (!PG_ARGISNULL(2))
+			appendStringInfoText(state, PG_GETARG_TEXT_PP(2));	/* delimiter */
+
+		appendStringInfoText(state, PG_GETARG_TEXT_PP(1));	/* value */
+	}
+
+	/*
+	 * The transition type for string_agg() is declared to be "internal", which
+	 * is a pass-by-value type the same size as a pointer.
+	 */
+	PG_RETURN_POINTER(state);
+}
+
+Datum
+string_agg_finalfn(PG_FUNCTION_ARGS)
+{
+	StringInfo		state;
+
+	if (PG_ARGISNULL(0))
+		PG_RETURN_NULL();
+
+	/* cannot be called directly because of internal-type argument */
+	Assert(fcinfo->context &&
+		   (IsA(fcinfo->context, AggState) ||
+			IsA(fcinfo->context, WindowAggState)));
+
+	state = (StringInfo) PG_GETARG_POINTER(0);
+	if (state != NULL)
+		PG_RETURN_TEXT_P(cstring_to_text(state->data));
+	else
+		PG_RETURN_NULL();
+}

src/include/catalog/catversion.h

@@ -37,7 +37,7 @@
  * Portions Copyright (c) 1996-2010, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/catalog/catversion.h,v 1.581 2010/01/28 23:21:12 petere Exp $
+ * $PostgreSQL: pgsql/src/include/catalog/catversion.h,v 1.582 2010/02/01 03:14:43 itagaki Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -53,6 +53,6 @@
  */
 
 /*							yyyymmddN */
-#define CATALOG_VERSION_NO	201001282
+#define CATALOG_VERSION_NO	201002011
 
 #endif

src/include/catalog/pg_aggregate.h

@@ -8,7 +8,7 @@
  * Portions Copyright (c) 1996-2010, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/catalog/pg_aggregate.h,v 1.70 2010/01/05 01:06:56 tgl Exp $
+ * $PostgreSQL: pgsql/src/include/catalog/pg_aggregate.h,v 1.71 2010/02/01 03:14:43 itagaki Exp $
  *
  * NOTES
  *	  the genbki.pl script reads this file and generates .bki
@@ -223,6 +223,10 @@ DATA(insert ( 2901 xmlconcat2	  -					0	142		_null_ ));
 /* array */
 DATA(insert ( 2335	array_agg_transfn	array_agg_finalfn		0	2281	_null_ ));
 
+/* text */
+DATA(insert (3537	string_agg_transfn			string_agg_finalfn	0	2281	_null_ ));
+DATA(insert (3538	string_agg_delim_transfn	string_agg_finalfn	0	2281	_null_ ));
+
 /*
  * prototypes for functions in pg_aggregate.c
  */

src/include/catalog/pg_proc.h

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2010, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/catalog/pg_proc.h,v 1.566 2010/01/28 14:25:41 mha Exp $
+ * $PostgreSQL: pgsql/src/include/catalog/pg_proc.h,v 1.567 2010/02/01 03:14:44 itagaki Exp $
  *
  * NOTES
  *	  The script catalog/genbki.pl reads this file and generates .bki
@@ -2829,6 +2829,16 @@ DATA(insert OID = 2816 (  float8_covar_samp			PGNSP PGUID 12 1 0 0 f f f t f i 1
 DESCR("COVAR_SAMP(double, double) aggregate final function");
 DATA(insert OID = 2817 (  float8_corr				PGNSP PGUID 12 1 0 0 f f f t f i 1 0 701 "1022" _null_ _null_ _null_ _null_ float8_corr _null_ _null_ _null_ ));
 DESCR("CORR(double, double) aggregate final function");
+DATA(insert OID = 3534 (  string_agg_transfn		PGNSP PGUID 12 1 0 0 f f f f f i 2 0 2281 "2281 25" _null_ _null_ _null_ _null_ string_agg_transfn _null_ _null_ _null_ ));
+DESCR("string_agg(text) transition function");
+DATA(insert OID = 3535 (  string_agg_delim_transfn	PGNSP PGUID 12 1 0 0 f f f f f i 3 0 2281 "2281 25 25" _null_ _null_ _null_ _null_ string_agg_delim_transfn _null_ _null_ _null_ ));
+DESCR("string_agg(text, text) transition function");
+DATA(insert OID = 3536 (  string_agg_finalfn		PGNSP PGUID 12 1 0 0 f f f f f i 1 0 25 "2281" _null_ _null_ _null_ _null_ string_agg_finalfn _null_ _null_ _null_ ));
+DESCR("string_agg final function");
+DATA(insert OID = 3537 (  string_agg				PGNSP PGUID 12 1 0 0 t f f f f i 1 0 25 "25" _null_ _null_ _null_ _null_ aggregate_dummy _null_ _null_ _null_ ));
+DESCR("concatenate aggregate input into an string");
+DATA(insert OID = 3538 (  string_agg				PGNSP PGUID 12 1 0 0 t f f f f i 2 0 25 "25 25" _null_ _null_ _null_ _null_ aggregate_dummy _null_ _null_ _null_ ));
+DESCR("concatenate aggregate input into an string with delimiter");
 
 /* To ASCII conversion */
 DATA(insert OID = 1845 ( to_ascii	PGNSP PGUID 12 1 0 0 f f f t f i 1 0 25 "25" _null_ _null_ _null_ _null_	to_ascii_default _null_ _null_ _null_ ));

src/include/utils/builtins.h

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2010, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/utils/builtins.h,v 1.345 2010/01/25 20:55:32 tgl Exp $
+ * $PostgreSQL: pgsql/src/include/utils/builtins.h,v 1.346 2010/02/01 03:14:45 itagaki Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -724,6 +724,10 @@ extern Datum unknownsend(PG_FUNCTION_ARGS);
 
 extern Datum pg_column_size(PG_FUNCTION_ARGS);
 
+extern Datum string_agg_transfn(PG_FUNCTION_ARGS);
+extern Datum string_agg_delim_transfn(PG_FUNCTION_ARGS);
+extern Datum string_agg_finalfn(PG_FUNCTION_ARGS);
+
 /* version.c */
 extern Datum pgsql_version(PG_FUNCTION_ARGS);
 
@@ -772,6 +776,9 @@ extern Datum translate(PG_FUNCTION_ARGS);
 extern Datum chr (PG_FUNCTION_ARGS);
 extern Datum repeat(PG_FUNCTION_ARGS);
 extern Datum ascii(PG_FUNCTION_ARGS);
+extern Datum string_agg_transfn(PG_FUNCTION_ARGS);
+extern Datum string_agg_delim_transfn(PG_FUNCTION_ARGS);
+extern Datum string_agg_finalfn(PG_FUNCTION_ARGS);
 
 /* inet_net_ntop.c */
 extern char *inet_net_ntop(int af, const void *src, int bits,

src/test/regress/expected/aggregates.out

@@ -799,3 +799,34 @@ select aggfns(distinct a,a,c order by a,b)
 ERROR:  in an aggregate with DISTINCT, ORDER BY expressions must appear in argument list
 LINE 1: select aggfns(distinct a,a,c order by a,b)
                                                 ^
+-- string_agg tests
+select string_agg(a) from (values('aaaa'),('bbbb'),('cccc')) g(a);
+  string_agg  
+--------------
+ aaaabbbbcccc
+(1 row)
+
+select string_agg(a,',') from (values('aaaa'),('bbbb'),('cccc')) g(a);
+   string_agg   
+----------------
+ aaaa,bbbb,cccc
+(1 row)
+
+select string_agg(a,',') from (values('aaaa'),(null),('bbbb'),('cccc')) g(a);
+   string_agg   
+----------------
+ aaaa,bbbb,cccc
+(1 row)
+
+select string_agg(a,',') from (values(null),(null),('bbbb'),('cccc')) g(a);
+ string_agg 
+------------
+ bbbb,cccc
+(1 row)
+
+select string_agg(a,',') from (values(null),(null)) g(a);
+ string_agg 
+------------
+ 
+(1 row)
+

src/test/regress/sql/aggregates.sql

@@ -355,3 +355,10 @@ select aggfns(distinct a,b,c order by a,b,i,c)
   from (values (1,1,'foo')) v(a,b,c), generate_series(1,2) i;
 select aggfns(distinct a,a,c order by a,b)
   from (values (1,1,'foo')) v(a,b,c), generate_series(1,2) i;
+
+-- string_agg tests
+select string_agg(a) from (values('aaaa'),('bbbb'),('cccc')) g(a);
+select string_agg(a,',') from (values('aaaa'),('bbbb'),('cccc')) g(a);
+select string_agg(a,',') from (values('aaaa'),(null),('bbbb'),('cccc')) g(a);
+select string_agg(a,',') from (values(null),(null),('bbbb'),('cccc')) g(a);
+select string_agg(a,',') from (values(null),(null)) g(a);