Implement RETURN QUERY for PL/PgSQL. This provides some convenient syntax

sugar for PL/PgSQL set-returning functions that want to return the result
of evaluating a query; it should also be more efficient than repeated
RETURN NEXT statements. Based on an earlier patch from Pavel Stehule.

doc/src/sgml/plpgsql.sgml

-<!-- $PostgreSQL: pgsql/doc/src/sgml/plpgsql.sgml,v 1.115 2007/07/16 17:01:10 tgl Exp $ -->
+<!-- $PostgreSQL: pgsql/doc/src/sgml/plpgsql.sgml,v 1.116 2007/07/25 04:19:08 neilc Exp $ -->
 
 <chapter id="plpgsql"> 
   <title><application>PL/pgSQL</application> - <acronym>SQL</acronym> Procedural Language</title>
@@ -135,7 +135,9 @@
      <application>PL/pgSQL</> functions can also be declared to return
      a <quote>set</>, or table, of any data type they can return a single
      instance of.  Such a function generates its output by executing
-     <literal>RETURN NEXT</> for each desired element of the result set.
+     <command>RETURN NEXT</> for each desired element of the result
+     set, or by using <command>RETURN QUERY</> to output the result of
+     evaluating a query.
     </para>
 
     <para>
@@ -1349,52 +1351,69 @@ RETURN <replaceable>expression</replaceable>;
     </sect3>
 
     <sect3>
-     <title><command>RETURN NEXT</></title>
+     <title><command>RETURN NEXT</> and <command>RETURN QUERY</command></title>
+    <indexterm>
+     <primary>RETURN NEXT</primary>
+     <secondary>in PL/PgSQL</secondary>
+    </indexterm>
+    <indexterm>
+     <primary>RETURN QUERY</primary>
+     <secondary>in PL/PgSQL</secondary>
+    </indexterm>
 
 <synopsis>
 RETURN NEXT <replaceable>expression</replaceable>;
+RETURN QUERY <replaceable>query</replaceable>;
 </synopsis>
 
      <para>
       When a <application>PL/pgSQL</> function is declared to return
       <literal>SETOF <replaceable>sometype</></literal>, the procedure
       to follow is slightly different.  In that case, the individual
-      items to return are specified in <command>RETURN NEXT</command>
-      commands, and then a final <command>RETURN</command> command
-      with no argument is used to indicate that the function has
-      finished executing.  <command>RETURN NEXT</command> can be used
-      with both scalar and composite data types; with a composite result
-      type, an entire <quote>table</quote> of results will be returned.
-     </para>
-
-     <para>
-      <command>RETURN NEXT</command> does not actually return from the
-      function &mdash; it simply saves away the value of the expression.
-      Execution then continues with the next statement in
-      the <application>PL/pgSQL</> function.  As successive
-      <command>RETURN NEXT</command> commands are executed, the result
-      set is built up.  A final <command>RETURN</command>, which should
-      have no argument, causes control to exit the function (or you can
-      just let control reach the end of the function).
+      items to return are specified by a sequence of <command>RETURN
+      NEXT</command> or <command>RETURN QUERY</command> commands, and
+      then a final <command>RETURN</command> command with no argument
+      is used to indicate that the function has finished executing.
+      <command>RETURN NEXT</command> can be used with both scalar and
+      composite data types; with a composite result type, an entire
+      <quote>table</quote> of results will be returned.
+      <command>RETURN QUERY</command> appends the results of executing
+      a query to the function's result set. <command>RETURN
+      NEXT</command> and <command>RETURN QUERY</command> can be freely
+      intermixed in a single set-returning function, in which case
+      their results will be concatenated.
+     </para>
+
+     <para>
+      <command>RETURN NEXT</command> and <command>RETURN
+      QUERY</command> do not actually return from the function &mdash;
+      they simply append zero or more rows to the function's result
+      set.  Execution then continues with the next statement in the
+      <application>PL/pgSQL</> function.  As successive
+      <command>RETURN NEXT</command> or <command>RETURN
+      QUERY</command> commands are executed, the result set is built
+      up.  A final <command>RETURN</command>, which should have no
+      argument, causes control to exit the function (or you can just
+      let control reach the end of the function).
      </para>
 
      <para>
       If you declared the function with output parameters, write just
       <command>RETURN NEXT</command> with no expression.  On each
-      execution, the current values
-      of the output parameter variable(s) will be saved for eventual return
-      as a row of the result.
-      Note that you must declare the function as returning
-      <literal>SETOF record</literal> when there are
-      multiple output parameters, or
-      <literal>SETOF <replaceable>sometype</></literal> when there is
-      just one output parameter of type <replaceable>sometype</>, in
-      order to create a set-returning function with output parameters.
+      execution, the current values of the output parameter
+      variable(s) will be saved for eventual return as a row of the
+      result.  Note that you must declare the function as returning
+      <literal>SETOF record</literal> when there are multiple output
+      parameters, or <literal>SETOF <replaceable>sometype</></literal>
+      when there is just one output parameter of type
+      <replaceable>sometype</>, in order to create a set-returning
+      function with output parameters.
      </para>
 
      <para>
-      Functions that use <command>RETURN NEXT</command> should be
-      called in the following fashion:
+      Functions that use <command>RETURN NEXT</command> or
+      <command>RETURN QUERY</command> should be called in the
+      following fashion:
 
 <programlisting>
 SELECT * FROM some_func();
@@ -1407,7 +1426,7 @@ SELECT * FROM some_func();
      <note>
       <para>
        The current implementation of <command>RETURN NEXT</command>
-       for <application>PL/pgSQL</> stores the entire result set
+       and <command>RETURN QUERY</command> stores the entire result set
        before returning from the function, as discussed above.  That
        means that if a <application>PL/pgSQL</> function produces a
        very large result set, performance might be poor: data will be

src/pl/plpgsql/src/gram.y

@@ -9,7 +9,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/pl/plpgsql/src/gram.y,v 1.104 2007/07/16 17:01:10 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/pl/plpgsql/src/gram.y,v 1.105 2007/07/25 04:19:08 neilc Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -32,6 +32,7 @@ static	PLpgSQL_stmt	*make_execsql_stmt(const char *sqlstart, int lineno);
 static	PLpgSQL_stmt_fetch *read_fetch_direction(void);
 static	PLpgSQL_stmt	*make_return_stmt(int lineno);
 static	PLpgSQL_stmt	*make_return_next_stmt(int lineno);
+static	PLpgSQL_stmt	*make_return_query_stmt(int lineno);
 static	void			 check_assignable(PLpgSQL_datum *datum);
 static	void			 read_into_target(PLpgSQL_rec **rec, PLpgSQL_row **row,
 										  bool *strict);
@@ -187,6 +188,7 @@ static	void			 check_labels(const char *start_label,
 %token	K_NULL
 %token	K_OPEN
 %token	K_OR
+%token	K_QUERY
 %token	K_PERFORM
 %token	K_ROW_COUNT
 %token	K_RAISE
@@ -1171,6 +1173,10 @@ stmt_return		: K_RETURN lno
 						{
 							$$ = make_return_next_stmt($2);
 						}
+						else if (tok == K_QUERY)
+						{
+							$$ = make_return_query_stmt($2);
+						}
 						else
 						{
 							plpgsql_push_back_token(tok);
@@ -2104,7 +2110,8 @@ make_return_stmt(int lineno)
 	if (plpgsql_curr_compile->fn_retset)
 	{
 		if (yylex() != ';')
-			yyerror("RETURN cannot have a parameter in function returning set; use RETURN NEXT");
+			yyerror("RETURN cannot have a parameter in function "
+					"returning set; use RETURN NEXT or RETURN QUERY");
 	}
 	else if (plpgsql_curr_compile->out_param_varno >= 0)
 	{
@@ -2200,6 +2207,23 @@ make_return_next_stmt(int lineno)
 }
 
 
+static PLpgSQL_stmt *
+make_return_query_stmt(int lineno)
+{
+	PLpgSQL_stmt_return_query *new;
+
+	if (!plpgsql_curr_compile->fn_retset)
+		yyerror("cannot use RETURN QUERY in a non-SETOF function");
+
+	new = palloc0(sizeof(PLpgSQL_stmt_return_query));
+	new->cmd_type = PLPGSQL_STMT_RETURN_QUERY;
+	new->lineno = lineno;
+	new->query = read_sql_construct(';', 0, ")", "", false, true, NULL);
+
+	return (PLpgSQL_stmt *) new;
+}
+
+
 static void
 check_assignable(PLpgSQL_datum *datum)
 {

src/pl/plpgsql/src/pl_exec.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/pl/plpgsql/src/pl_exec.c,v 1.198 2007/07/15 02:15:04 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/pl/plpgsql/src/pl_exec.c,v 1.199 2007/07/25 04:19:08 neilc Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -105,6 +105,8 @@ static int exec_stmt_return(PLpgSQL_execstate *estate,
 				 PLpgSQL_stmt_return *stmt);
 static int exec_stmt_return_next(PLpgSQL_execstate *estate,
 					  PLpgSQL_stmt_return_next *stmt);
+static int exec_stmt_return_query(PLpgSQL_execstate *estate,
+					  PLpgSQL_stmt_return_query *stmt);
 static int exec_stmt_raise(PLpgSQL_execstate *estate,
 				PLpgSQL_stmt_raise *stmt);
 static int exec_stmt_execsql(PLpgSQL_execstate *estate,
@@ -1244,6 +1246,10 @@ exec_stmt(PLpgSQL_execstate *estate, PLpgSQL_stmt *stmt)
 			rc = exec_stmt_return_next(estate, (PLpgSQL_stmt_return_next *) stmt);
 			break;
 
+		case PLPGSQL_STMT_RETURN_QUERY:
+			rc = exec_stmt_return_query(estate, (PLpgSQL_stmt_return_query *) stmt);
+			break;
+
 		case PLPGSQL_STMT_RAISE:
 			rc = exec_stmt_raise(estate, (PLpgSQL_stmt_raise *) stmt);
 			break;
@@ -2137,6 +2143,59 @@ exec_stmt_return_next(PLpgSQL_execstate *estate,
 	return PLPGSQL_RC_OK;
 }
 
+/* ----------
+ * exec_stmt_return_query		Evaluate a query and add it to the
+ *								list of tuples returned by the current
+ *								SRF.
+ * ----------
+ */
+static int
+exec_stmt_return_query(PLpgSQL_execstate *estate,
+					   PLpgSQL_stmt_return_query *stmt)
+{
+	Portal 		portal;
+
+	if (!estate->retisset)
+		ereport(ERROR,
+				(errcode(ERRCODE_SYNTAX_ERROR),
+				 errmsg("cannot use RETURN QUERY in a non-SETOF function")));
+
+	if (estate->tuple_store == NULL)
+		exec_init_tuple_store(estate);
+
+	exec_run_select(estate, stmt->query, 0, &portal);
+
+	if (!compatible_tupdesc(estate->rettupdesc, portal->tupDesc))
+		ereport(ERROR,
+				(errcode(ERRCODE_DATATYPE_MISMATCH),
+				 errmsg("structure of query does not match function result type")));
+
+	while (true)
+	{
+		MemoryContext 	old_cxt;
+		int 			i;
+
+		SPI_cursor_fetch(portal, true, 50);
+		if (SPI_processed == 0)
+			break;
+
+		old_cxt = MemoryContextSwitchTo(estate->tuple_store_cxt);
+		for (i = 0; i < SPI_processed; i++)
+		{
+			HeapTuple tuple = SPI_tuptable->vals[i];
+			tuplestore_puttuple(estate->tuple_store, tuple);
+		}
+		MemoryContextSwitchTo(old_cxt);
+
+		SPI_freetuptable(SPI_tuptable);
+	}
+
+	SPI_freetuptable(SPI_tuptable);
+	SPI_cursor_close(portal);
+
+	return PLPGSQL_RC_OK;
+}
+
 static void
 exec_init_tuple_store(PLpgSQL_execstate *estate)
 {

src/pl/plpgsql/src/pl_funcs.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/pl/plpgsql/src/pl_funcs.c,v 1.62 2007/07/20 16:23:34 petere Exp $
+ *	  $PostgreSQL: pgsql/src/pl/plpgsql/src/pl_funcs.c,v 1.63 2007/07/25 04:19:08 neilc Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -443,6 +443,8 @@ plpgsql_stmt_typename(PLpgSQL_stmt *stmt)
 			return "RETURN";
 		case PLPGSQL_STMT_RETURN_NEXT:
 			return "RETURN NEXT";
+		case PLPGSQL_STMT_RETURN_QUERY:
+			return "RETURN QUERY";
 		case PLPGSQL_STMT_RAISE:
 			return "RAISE";
 		case PLPGSQL_STMT_EXECSQL:
@@ -484,6 +486,7 @@ static void dump_fors(PLpgSQL_stmt_fors *stmt);
 static void dump_exit(PLpgSQL_stmt_exit *stmt);
 static void dump_return(PLpgSQL_stmt_return *stmt);
 static void dump_return_next(PLpgSQL_stmt_return_next *stmt);
+static void dump_return_query(PLpgSQL_stmt_return_query *stmt);
 static void dump_raise(PLpgSQL_stmt_raise *stmt);
 static void dump_execsql(PLpgSQL_stmt_execsql *stmt);
 static void dump_dynexecute(PLpgSQL_stmt_dynexecute *stmt);
@@ -542,6 +545,9 @@ dump_stmt(PLpgSQL_stmt *stmt)
 		case PLPGSQL_STMT_RETURN_NEXT:
 			dump_return_next((PLpgSQL_stmt_return_next *) stmt);
 			break;
+		case PLPGSQL_STMT_RETURN_QUERY:
+			dump_return_query((PLpgSQL_stmt_return_query *) stmt);
+			break;
 		case PLPGSQL_STMT_RAISE:
 			dump_raise((PLpgSQL_stmt_raise *) stmt);
 			break;
@@ -878,6 +884,15 @@ dump_return_next(PLpgSQL_stmt_return_next *stmt)
 	printf("\n");
 }
 
+static void
+dump_return_query(PLpgSQL_stmt_return_query *stmt)
+{
+	dump_ind();
+	printf("RETURN QUERY ");
+	dump_expr(stmt->query);
+	printf("\n");
+}
+
 static void
 dump_raise(PLpgSQL_stmt_raise *stmt)
 {

src/pl/plpgsql/src/plpgsql.h

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/pl/plpgsql/src/plpgsql.h,v 1.90 2007/07/16 17:01:11 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/pl/plpgsql/src/plpgsql.h,v 1.91 2007/07/25 04:19:09 neilc Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -83,6 +83,7 @@ enum
 	PLPGSQL_STMT_EXIT,
 	PLPGSQL_STMT_RETURN,
 	PLPGSQL_STMT_RETURN_NEXT,
+	PLPGSQL_STMT_RETURN_QUERY,
 	PLPGSQL_STMT_RAISE,
 	PLPGSQL_STMT_EXECSQL,
 	PLPGSQL_STMT_DYNEXECUTE,
@@ -493,6 +494,13 @@ typedef struct
 	int			retvarno;
 } PLpgSQL_stmt_return_next;
 
+typedef struct
+{								/* RETURN QUERY statement */
+	int			cmd_type;
+	int			lineno;
+	PLpgSQL_expr *query;
+} PLpgSQL_stmt_return_query;
+
 typedef struct
 {								/* RAISE statement			*/
 	int			cmd_type;

src/pl/plpgsql/src/scan.l

@@ -9,7 +9,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/pl/plpgsql/src/scan.l,v 1.57 2007/04/29 01:21:09 neilc Exp $
+ *	  $PostgreSQL: pgsql/src/pl/plpgsql/src/scan.l,v 1.58 2007/07/25 04:19:09 neilc Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -151,6 +151,7 @@ null			{ return K_NULL;			}
 open			{ return K_OPEN;			}
 or				{ return K_OR;				}
 perform			{ return K_PERFORM;			}
+query			{ return K_QUERY;			}
 raise			{ return K_RAISE;			}
 rename			{ return K_RENAME;			}
 result_oid		{ return K_RESULT_OID;		}

src/test/regress/expected/plpgsql.out

@@ -3079,3 +3079,52 @@ NOTICE:  innerblock.param1 = 2
 (1 row)
 
 drop function pl_qual_names(int);
+-- tests for RETURN QUERY
+create function ret_query1(out int, out int) returns setof record as $$
+begin
+    $1 := -1;
+    $2 := -2;
+    return next;
+    return query select x + 1, x * 10 from generate_series(0, 10) s (x);
+    return next;
+end;
+$$ language plpgsql;
+select * from ret_query1();
+ column1 | column2 
+---------+---------
+      -1 |      -2
+       1 |       0
+       2 |      10
+       3 |      20
+       4 |      30
+       5 |      40
+       6 |      50
+       7 |      60
+       8 |      70
+       9 |      80
+      10 |      90
+      11 |     100
+      -1 |      -2
+(13 rows)
+
+create type record_type as (x text, y int, z boolean);
+create or replace function ret_query2(lim int) returns setof record_type as $$
+begin
+    return query select md5(s.x::text), s.x, s.x > 0
+                 from generate_series(-8, lim) s (x) where s.x % 2 = 0;
+end;
+$$ language plpgsql;
+select * from ret_query2(8);
+                x                 | y  | z 
+----------------------------------+----+---
+ a8d2ec85eaf98407310b72eb73dda247 | -8 | f
+ 596a3d04481816330f07e4f97510c28f | -6 | f
+ 0267aaf632e87a63288a08331f22c7c3 | -4 | f
+ 5d7b9adcbe1c629ec722529dd12e5129 | -2 | f
+ cfcd208495d565ef66e7dff9f98764da |  0 | f
+ c81e728d9d4c2f636f067f89cc14862c |  2 | t
+ a87ff679a2f3e71d9181a67b7542122c |  4 | t
+ 1679091c5a880faf6fb5e6087eb1b2dc |  6 | t
+ c9f0f895fb98ab9159f51fd0297e236d |  8 | t
+(9 rows)
+

src/test/regress/sql/plpgsql.sql

@@ -2557,3 +2557,27 @@ $$ language plpgsql;
 select pl_qual_names(42);
 
 drop function pl_qual_names(int);
+
+-- tests for RETURN QUERY
+create function ret_query1(out int, out int) returns setof record as $$
+begin
+    $1 := -1;
+    $2 := -2;
+    return next;
+    return query select x + 1, x * 10 from generate_series(0, 10) s (x);
+    return next;
+end;
+$$ language plpgsql;
+
+select * from ret_query1();
+
+create type record_type as (x text, y int, z boolean);
+
+create or replace function ret_query2(lim int) returns setof record_type as $$
+begin
+    return query select md5(s.x::text), s.x, s.x > 0
+                 from generate_series(-8, lim) s (x) where s.x % 2 = 0;
+end;
+$$ language plpgsql;
+
+select * from ret_query2(8);
\ No newline at end of file