Add generate_subscripts, a series-generation function which generates an

array's subscripts.

Pavel Stehule, some editorialization by me.

doc/src/sgml/array.sgml

-<!-- $PostgreSQL: pgsql/doc/src/sgml/array.sgml,v 1.65 2008/04/27 04:33:27 alvherre Exp $ -->
+<!-- $PostgreSQL: pgsql/doc/src/sgml/array.sgml,v 1.66 2008/04/28 14:48:57 alvherre Exp $ -->
 
 <sect1 id="arrays">
  <title>Arrays</title>
@@ -542,6 +542,21 @@ SELECT * FROM sal_emp WHERE 10000 = ALL (pay_by_quarter);
 
  </para>
 
+ <para>
+  Alternatively, the <function>generate_subscripts</> function can be used.
+  For example:
+
+<programlisting>
+SELECT * FROM
+   (SELECT pay_by_quarter,
+           generate_subscripts(pay_by_quarter, 1) AS s
+      FROM sal_emp) AS foo
+ WHERE pay_by_quarter[s] = 10000;
+</programlisting>
+
+  This function is described in <xref linkend="functions-srf-subscripts">.
+ </para>
+
  <tip>
   <para>
    Arrays are not sets; searching for specific array elements

doc/src/sgml/func.sgml

-<!-- $PostgreSQL: pgsql/doc/src/sgml/func.sgml,v 1.433 2008/04/17 20:56:41 momjian Exp $ -->
+<!-- $PostgreSQL: pgsql/doc/src/sgml/func.sgml,v 1.434 2008/04/28 14:48:57 alvherre Exp $ -->
 
  <chapter id="functions">
   <title>Functions and Operators</title>
@@ -10613,7 +10613,8 @@ AND
   <para>
    This section describes functions that possibly return more than one row.
    Currently the only functions in this class are series generating functions,
-   as detailed in <xref linkend="functions-srf-series">.
+   as detailed in <xref linkend="functions-srf-series"> and
+   <xref linkend="functions-srf-subscripts">.
   </para>
 
   <table id="functions-srf-series">
@@ -10691,6 +10692,99 @@ select current_date + s.a as dates from generate_series(0,14,7) as s(a);
 (3 rows)
 </programlisting>
   </para>
+
+  <table id="functions-srf-subscripts">
+
+  <indexterm>
+   <primary>generate_subscripts</primary>
+  </indexterm>
+
+   <title>Subscripts Generating Functions</title>
+   <tgroup cols="3">
+    <thead>
+     <row>
+      <entry>Function</entry>
+      <entry>Return Type</entry>
+      <entry>Description</entry>
+     </row>
+    </thead>
+
+    <tbody>
+     <row>
+      <entry><literal><function>generate_subscripts</function>(<parameter>array annyarray</parameter>, <parameter>dim int</parameter>)</literal></entry>
+      <entry><type>setof int</type></entry>
+      <entry>
+       Generate a series comprising the given array's subscripts.
+      </entry>
+     </row>
+
+     <row>
+      <entry><literal><function>generate_subscripts</function>(<parameter>array annyarray</parameter>, <parameter>dim int</parameter>, <parameter>reverse boolean</parameter>)</literal></entry>
+      <entry><type>setof int</type></entry>
+      <entry>
+       Generate a series comprising the given array's subscripts. When
+       <parameter>reverse</parameter> is true, the series is returned in
+       reverse order.
+      </entry>
+     </row>
+
+    </tbody>
+   </tgroup>
+  </table>
+
+  <para>
+   Zero rows are returned for arrays that do not have the requested dimension,
+   or for NULL arrays (but valid subscripts are returned for NULL array
+   elements.) Some examples follow:
+<programlisting>
+-- basic usage
+select generate_subscripts('{NULL,1,NULL,2}'::int[], 1) as s;
+ s 
+---
+ 1
+ 2
+ 3
+ 4
+(4 rows)
+
+-- presenting an array, the subscript and the subscripted
+-- value requires a subquery
+select * from arrays;
+         a          
+--------------------
+ {-1,-2}
+ {100,200}
+(2 rows)
+
+select a as array, s as subscript, a[s] as value
+from (select generate_subscripts(a, 1) as s, a from arrays) foo;
+   array   | subscript | value 
+-----------+-----------+-------
+ {-1,-2}   |         1 |    -1
+ {-1,-2}   |         2 |    -2
+ {100,200} |         1 |   100
+ {100,200} |         2 |   200
+(4 rows)
+
+-- unnest a 2D array
+create or replace function unnest2(anyarray)
+returns setof anyelement as $$
+select $1[i][j] 
+   from generate_subscripts($1,1) g1(i),
+        generate_subscripts($1,2) g2(j);
+$$ language sql immutable;
+CREATE FUNCTION
+postgres=# select * from unnest2(array[[1,2],[3,4]]);
+ unnest2 
+---------
+       1
+       2
+       3
+       4
+(4 rows)
+</programlisting>
+  </para>
+
  </sect1>
 
  <sect1 id="functions-info">

src/backend/utils/adt/arrayfuncs.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/utils/adt/arrayfuncs.c,v 1.143 2008/04/11 22:52:05 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/utils/adt/arrayfuncs.c,v 1.144 2008/04/28 14:48:57 alvherre Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -17,6 +17,7 @@
 #include <ctype.h>
 
 #include "access/tupmacs.h"
+#include "funcapi.h"
 #include "libpq/pqformat.h"
 #include "parser/parse_coerce.h"
 #include "utils/array.h"
@@ -4231,3 +4232,86 @@ array_smaller(PG_FUNCTION_ARGS)
 
 	PG_RETURN_ARRAYTYPE_P(result);
 }
+
+
+typedef struct generate_subscripts_fctx
+{
+        int4    lower;
+        int4    upper;
+        bool    reverse;
+} generate_subscripts_fctx;
+
+/* 
+ * generate_subscripts(array anyarray, dim int [, reverse bool])
+ *		Returns all subscripts of the array for any dimension
+ */
+Datum
+generate_subscripts(PG_FUNCTION_ARGS)
+{
+	FuncCallContext *funcctx;
+	MemoryContext oldcontext;
+	generate_subscripts_fctx *fctx;
+
+	/* stuff done only on the first call of the function */
+	if (SRF_IS_FIRSTCALL())
+	{
+		ArrayType *v = PG_GETARG_ARRAYTYPE_P(0);
+		int		reqdim = PG_GETARG_INT32(1);
+		int    *lb,
+			   *dimv;
+
+		/* create a function context for cross-call persistence */
+		funcctx = SRF_FIRSTCALL_INIT();
+
+		/* Sanity check: does it look like an array at all? */
+		if (ARR_NDIM(v) <= 0 || ARR_NDIM(v) > MAXDIM)
+			SRF_RETURN_DONE(funcctx);
+
+		/* Sanity check: was the requested dim valid */
+		if (reqdim <= 0 || reqdim > ARR_NDIM(v))
+			SRF_RETURN_DONE(funcctx);
+
+		/*
+		 * switch to memory context appropriate for multiple function calls
+		 */
+		oldcontext = MemoryContextSwitchTo(funcctx->multi_call_memory_ctx);
+		fctx = (generate_subscripts_fctx *) palloc(sizeof(generate_subscripts_fctx));
+
+		lb = ARR_LBOUND(v);
+		dimv = ARR_DIMS(v);
+
+		fctx->lower = lb[reqdim - 1];
+		fctx->upper = dimv[reqdim - 1] + lb[reqdim - 1] - 1;
+		fctx->reverse = (PG_NARGS() < 3) ? false : PG_GETARG_BOOL(2);
+
+		funcctx->user_fctx = fctx;
+
+		MemoryContextSwitchTo(oldcontext);
+	}
+
+	funcctx = SRF_PERCALL_SETUP();
+
+	fctx = funcctx->user_fctx;
+
+	if (fctx->lower <= fctx->upper)
+	{
+		if (!fctx->reverse)
+			SRF_RETURN_NEXT(funcctx, Int32GetDatum(fctx->lower++));
+		else
+			SRF_RETURN_NEXT(funcctx, Int32GetDatum(fctx->upper--));
+	}
+	else
+		/* done when there are no more elements left */
+		SRF_RETURN_DONE(funcctx);
+}
+
+/*
+ * generate_subscripts_nodir
+ *		Implements the 2-argument version of generate_subscripts
+ */
+Datum
+generate_subscripts_nodir(PG_FUNCTION_ARGS)
+{
+	/* just call the other one -- it can handle both cases */
+	return generate_subscripts(fcinfo);
+}

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 1.492 2008/04/17 20:56:41 momjian Exp $
+ * $PostgreSQL: pgsql/src/include/catalog/pg_proc.h,v 1.493 2008/04/28 14:48:57 alvherre Exp $
  *
  * NOTES
  *	  The script catalog/genbki.sh reads this file and generates .bki
@@ -1010,6 +1010,11 @@ DATA(insert OID = 515 (  array_larger	   PGNSP PGUID 12 1 0 f f t f i 2 2277 "22
 DESCR("larger of two");
 DATA(insert OID = 516 (  array_smaller	   PGNSP PGUID 12 1 0 f f t f i 2 2277 "2277 2277" _null_ _null_ _null_ array_smaller - _null_ _null_ ));
 DESCR("smaller of two");
+DATA(insert OID = 1191 (  generate_subscripts PGNSP PGUID 12 1 1000 f f t t v 3 23 "2277 23 16" _null_ _null_ _null_ generate_subscripts - _null_ _null_ ));
+DESCR("array subscripts generator");
+DATA(insert OID = 1192 (  generate_subscripts PGNSP PGUID 12 1 1000 f f t t v 2 23 "2277 23" _null_ _null_ _null_ generate_subscripts_nodir - _null_ _null_ ));
+DESCR("array subscripts generator");
+
 
 DATA(insert OID = 760 (  smgrin			   PGNSP PGUID 12 1 0 f f t f s 1 210 "2275" _null_ _null_ _null_  smgrin - _null_ _null_ ));
 DESCR("I/O");

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 1.66 2008/01/01 19:45:59 momjian Exp $
+ * $PostgreSQL: pgsql/src/include/utils/array.h,v 1.67 2008/04/28 14:48:57 alvherre Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -200,6 +200,8 @@ extern Datum array_lower(PG_FUNCTION_ARGS);
 extern Datum array_upper(PG_FUNCTION_ARGS);
 extern Datum array_larger(PG_FUNCTION_ARGS);
 extern Datum array_smaller(PG_FUNCTION_ARGS);
+extern Datum generate_subscripts(PG_FUNCTION_ARGS);
+extern Datum generate_subscripts_nodir(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

@@ -903,3 +903,33 @@ select c2[2].f2 from comptable;
 drop type _comptype;
 drop table comptable;
 drop type comptype;
+create or replace function unnest1(anyarray) 
+returns setof anyelement as $$
+select $1[s] from generate_subscripts($1,1) g(s);
+$$ language sql immutable;
+create or replace function unnest2(anyarray) 
+returns setof anyelement as $$
+select $1[s1][s2] from generate_subscripts($1,1) g1(s1),
+                   generate_subscripts($1,2) g2(s2);
+$$ language sql immutable;
+select * from unnest1(array[1,2,3]);
+ unnest1 
+---------
+       1
+       2
+       3
+(3 rows)
+
+select * from unnest2(array[[1,2,3],[4,5,6]]);
+ unnest2 
+---------
+       1
+       2
+       3
+       4
+       5
+       6
+(6 rows)
+
+drop function unnest1(anyarray);
+drop function unnest2(anyarray);

src/test/regress/sql/arrays.sql

@@ -340,3 +340,20 @@ select c2[2].f2 from comptable;
 drop type _comptype;
 drop table comptable;
 drop type comptype;
+
+create or replace function unnest1(anyarray) 
+returns setof anyelement as $$
+select $1[s] from generate_subscripts($1,1) g(s);
+$$ language sql immutable;
+
+create or replace function unnest2(anyarray) 
+returns setof anyelement as $$
+select $1[s1][s2] from generate_subscripts($1,1) g1(s1),
+                   generate_subscripts($1,2) g2(s2);
+$$ language sql immutable;
+
+select * from unnest1(array[1,2,3]);
+select * from unnest2(array[[1,2,3],[4,5,6]]);
+
+drop function unnest1(anyarray);
+drop function unnest2(anyarray);