Implement the basic form of UNNEST, ie unnest(anyarray) returns setof

anyelement.  This lacks the WITH ORDINALITY option, as well as the multiple
input arrays option added in the most recent SQL specs.  But it's still a
pretty useful subset of the spec's functionality, and it is enough to
allow obsoleting contrib/intagg.

doc/src/sgml/func.sgml

-<!-- $PostgreSQL: pgsql/doc/src/sgml/func.sgml,v 1.459 2008/11/13 23:01:09 tgl Exp $ -->
+<!-- $PostgreSQL: pgsql/doc/src/sgml/func.sgml,v 1.460 2008/11/14 00:51:46 tgl Exp $ -->
 
  <chapter id="functions">
   <title>Functions and Operators</title>
@@ -9482,6 +9482,17 @@ SELECT NULLIF(value, '(none)') ...
         <entry><literal>string_to_array('xx~^~yy~^~zz', '~^~')</literal></entry>
         <entry><literal>{xx,yy,zz}</literal></entry>
        </row>
+       <row>
+        <entry>
+         <literal>
+          <function>unnest</function>(<type>anyarray</type>)
+         </literal>
+        </entry>
+        <entry><type>setof anyelement</type></entry>
+        <entry>expand an array to a set of rows</entry>
+        <entry><literal>unnest(ARRAY[1,2])</literal></entry>
+        <entry><literal>1</literal><para><literal>2</literal></para> (2 rows)</entry>
+       </row>
       </tbody>
      </tgroup>
     </table>

src/backend/utils/adt/arrayfuncs.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/utils/adt/arrayfuncs.c,v 1.149 2008/11/12 13:09:27 petere Exp $
+ *	  $PostgreSQL: pgsql/src/backend/utils/adt/arrayfuncs.c,v 1.150 2008/11/14 00:51:46 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -4635,3 +4635,107 @@ array_fill_internal(ArrayType *dims, ArrayType *lbs,
 
 	return result;
 }
+
+
+/*
+ * UNNEST
+ */
+Datum
+array_unnest(PG_FUNCTION_ARGS)
+{
+	typedef struct
+	{
+		ArrayType *arr;
+		int		nextelem;
+		int		numelems;
+		char   *elemdataptr;	/* this moves with nextelem */
+		bits8  *arraynullsptr;	/* this does not */
+		int16	elmlen;
+		bool	elmbyval;
+		char	elmalign;
+	} array_unnest_fctx;
+
+	FuncCallContext *funcctx;
+	array_unnest_fctx *fctx;
+	MemoryContext oldcontext;
+
+	/* stuff done only on the first call of the function */
+	if (SRF_IS_FIRSTCALL())
+	{
+		ArrayType  *arr = PG_GETARG_ARRAYTYPE_P(0);
+
+		/* create a function context for cross-call persistence */
+		funcctx = SRF_FIRSTCALL_INIT();
+
+		/*
+		 * switch to memory context appropriate for multiple function calls
+		 */
+		oldcontext = MemoryContextSwitchTo(funcctx->multi_call_memory_ctx);
+
+		/* allocate memory for user context */
+		fctx = (array_unnest_fctx *) palloc(sizeof(array_unnest_fctx));
+
+		/*
+		 * Initialize state.  Note we assume that the originally passed
+		 * array will stick around for the whole call series.
+		 */
+		fctx->arr = arr;
+		fctx->nextelem = 0;
+		fctx->numelems = ArrayGetNItems(ARR_NDIM(arr), ARR_DIMS(arr));
+
+		fctx->elemdataptr = ARR_DATA_PTR(arr);
+		fctx->arraynullsptr = ARR_NULLBITMAP(arr);
+
+		get_typlenbyvalalign(ARR_ELEMTYPE(arr),
+							 &fctx->elmlen,
+							 &fctx->elmbyval,
+							 &fctx->elmalign);
+
+		funcctx->user_fctx = fctx;
+		MemoryContextSwitchTo(oldcontext);
+	}
+
+	/* stuff done on every call of the function */
+	funcctx = SRF_PERCALL_SETUP();
+	fctx = funcctx->user_fctx;
+
+	if (fctx->nextelem < fctx->numelems)
+	{
+		int		offset = fctx->nextelem++;
+		Datum	elem;
+
+		/*
+		 * Check for NULL array element
+		 */
+		if (array_get_isnull(fctx->arraynullsptr, offset))
+		{
+			fcinfo->isnull = true;
+			elem = (Datum) 0;
+			/* elemdataptr does not move */
+		}
+		else
+		{
+			/*
+			 * OK, get the element
+			 */
+			char   *ptr = fctx->elemdataptr;
+
+			fcinfo->isnull = false;
+			elem = ArrayCast(ptr, fctx->elmbyval, fctx->elmlen);
+
+			/*
+			 * Advance elemdataptr over it
+			 */
+			ptr = att_addlength_pointer(ptr, fctx->elmlen, ptr);
+			ptr = (char *) att_align_nominal(ptr, fctx->elmalign);
+			fctx->elemdataptr = ptr;
+		}
+
+		SRF_RETURN_NEXT(funcctx, elem);
+	}
+	else
+	{
+		/* do when there is no more left */
+		SRF_RETURN_DONE(funcctx);
+	}
+}

src/include/catalog/catversion.h

@@ -37,7 +37,7 @@
  * Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/catalog/catversion.h,v 1.505 2008/11/13 15:59:50 petere Exp $
+ * $PostgreSQL: pgsql/src/include/catalog/catversion.h,v 1.506 2008/11/14 00:51:46 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -53,6 +53,6 @@
  */
 
 /*							yyyymmddN */
-#define CATALOG_VERSION_NO	200811131
+#define CATALOG_VERSION_NO	200811132
 
 #endif

src/include/catalog/pg_proc.h

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/catalog/pg_proc.h,v 1.527 2008/11/13 15:59:50 petere Exp $
+ * $PostgreSQL: pgsql/src/include/catalog/pg_proc.h,v 1.528 2008/11/14 00:51:46 tgl Exp $
  *
  * NOTES
  *	  The script catalog/genbki.sh reads this file and generates .bki
@@ -1022,6 +1022,8 @@ DATA(insert OID = 1193 (  array_fill PGNSP PGUID 12 1 0 0 f f f f i 2 2277 "2283
 DESCR("array constructor with value");
 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_ ));
 DESCR("array constructor with value");
+DATA(insert OID = 2331 (  unnest		   PGNSP PGUID 12 1 100 0 f f t t i 1 2283 "2277" _null_ _null_ _null_ array_unnest _null_ _null_ _null_ ));
+DESCR("expand array to set of rows");
 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_ ));
 DESCR("array_agg transition function");
 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_ ));

src/include/utils/array.h

@@ -49,7 +49,7 @@
  * Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/utils/array.h,v 1.71 2008/11/13 15:59:50 petere Exp $
+ * $PostgreSQL: pgsql/src/include/utils/array.h,v 1.72 2008/11/14 00:51:47 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -206,6 +206,7 @@ extern Datum generate_subscripts(PG_FUNCTION_ARGS);
 extern Datum generate_subscripts_nodir(PG_FUNCTION_ARGS);
 extern Datum array_fill(PG_FUNCTION_ARGS);
 extern Datum array_fill_with_lower_bounds(PG_FUNCTION_ARGS);
+extern Datum array_unnest(PG_FUNCTION_ARGS);
 
 extern Datum array_ref(ArrayType *array, int nSubscripts, int *indx,
 		  int arraytyplen, int elmlen, bool elmbyval, char elmalign,

src/test/regress/expected/arrays.out

@@ -1161,3 +1161,65 @@ select array_agg(unique1) from tenk1 where unique1 < -15;
  
 (1 row)
 
+select unnest(array[1,2,3]);
+ unnest 
+--------
+      1
+      2
+      3
+(3 rows)
+
+select * from unnest(array[1,2,3]);
+ unnest 
+--------
+      1
+      2
+      3
+(3 rows)
+
+select unnest(array[1,2,3,4.5]::float8[]);
+ unnest 
+--------
+      1
+      2
+      3
+    4.5
+(4 rows)
+
+select unnest(array[1,2,3,4.5]::numeric[]);
+ unnest 
+--------
+      1
+      2
+      3
+    4.5
+(4 rows)
+
+select unnest(array[1,2,3,null,4,null,null,5,6]);
+ unnest 
+--------
+      1
+      2
+      3
+       
+      4
+       
+       
+      5
+      6
+(9 rows)
+
+select unnest(array[1,2,3,null,4,null,null,5,6]::text[]);
+ unnest 
+--------
+ 1
+ 2
+ 3
+ 
+ 4
+ 
+ 
+ 5
+ 6
+(9 rows)
+

src/test/regress/sql/arrays.sql

@@ -402,3 +402,10 @@ select array_agg(nullif(ten, 4)) from tenk1 where unique1 < 15;
 select cardinality(array_agg(unique1)) from tenk1 where unique1 < 15;
 select array_agg(unique1) from (select * from tenk1 order by unique1 asc) as tab where unique1 < 15;
 select array_agg(unique1) from tenk1 where unique1 < -15;
+
+select unnest(array[1,2,3]);
+select * from unnest(array[1,2,3]);
+select unnest(array[1,2,3,4.5]::float8[]);
+select unnest(array[1,2,3,4.5]::numeric[]);
+select unnest(array[1,2,3,null,4,null,null,5,6]);
+select unnest(array[1,2,3,null,4,null,null,5,6]::text[]);