Re-implement LIMIT/OFFSET as a plan node type, instead of a hack in

ExecutorRun.  This allows LIMIT to work in a view.  Also, LIMIT in a
cursor declaration will behave in a reasonable fashion, whereas before
it was overridden by the FETCH count.

src/backend/optimizer/plan/createplan.c

@@ -10,7 +10,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/optimizer/plan/createplan.c,v 1.98 2000/10/05 19:11:29 tgl Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/optimizer/plan/createplan.c,v 1.99 2000/10/26 21:36:09 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -1651,6 +1651,27 @@ make_setop(SetOpCmd cmd, List *tlist, Plan *lefttree,
 	return node;
 }
 
+Limit *
+make_limit(List *tlist, Plan *lefttree,
+		   Node *limitOffset, Node *limitCount)
+{
+	Limit	   *node = makeNode(Limit);
+	Plan	   *plan = &node->plan;
+
+	copy_plan_costsize(plan, lefttree);
+
+	plan->state = (EState *) NULL;
+	plan->targetlist = tlist;
+	plan->qual = NIL;
+	plan->lefttree = lefttree;
+	plan->righttree = NULL;
+
+	node->limitOffset = limitOffset;
+	node->limitCount = limitCount;
+
+	return node;
+}
+
 Result *
 make_result(List *tlist,
 			Node *resconstantqual,

src/backend/optimizer/plan/planner.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/optimizer/plan/planner.c,v 1.92 2000/10/05 19:11:29 tgl Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/optimizer/plan/planner.c,v 1.93 2000/10/26 21:36:09 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -341,8 +341,6 @@ is_simple_subquery(Query *subquery)
 	 */
 	if (subquery->rowMarks)
 		elog(ERROR, "FOR UPDATE is not supported in subselects");
-	if (subquery->limitOffset || subquery->limitCount)
-		elog(ERROR, "LIMIT is not supported in subselects");
 	/*
 	 * Can't currently pull up a query with setops.
 	 * Maybe after querytree redesign...
@@ -350,13 +348,16 @@ is_simple_subquery(Query *subquery)
 	if (subquery->setOperations)
 		return false;
 	/*
-	 * Can't pull up a subquery involving grouping, aggregation, or sorting.
+	 * Can't pull up a subquery involving grouping, aggregation, sorting,
+	 * or limiting.
 	 */
 	if (subquery->hasAggs ||
 		subquery->groupClause ||
 		subquery->havingQual ||
 		subquery->sortClause ||
-		subquery->distinctClause)
+		subquery->distinctClause ||
+		subquery->limitOffset ||
+		subquery->limitCount)
 		return false;
 	/*
 	 * Hack: don't try to pull up a subquery with an empty jointree.
@@ -831,7 +832,7 @@ union_planner(Query *parse,
 							}
 							else
 							{
-								/* It's a PARAM ... punt ... */
+								/* It's an expression ... punt ... */
 								tuple_fraction = 0.10;
 							}
 						}
@@ -839,9 +840,8 @@ union_planner(Query *parse,
 				}
 				else
 				{
-
 					/*
-					 * COUNT is a PARAM ... don't know exactly what the
+					 * COUNT is an expression ... don't know exactly what the
 					 * limit will be, but for lack of a better idea assume
 					 * 10% of the plan's result is wanted.
 					 */
@@ -1024,7 +1024,7 @@ union_planner(Query *parse,
 	}
 
 	/*
-	 * Finally, if there is a DISTINCT clause, add the UNIQUE node.
+	 * If there is a DISTINCT clause, add the UNIQUE node.
 	 */
 	if (parse->distinctClause)
 	{
@@ -1032,6 +1032,16 @@ union_planner(Query *parse,
 										   parse->distinctClause);
 	}
 
+	/*
+	 * Finally, if there is a LIMIT/OFFSET clause, add the LIMIT node.
+	 */
+	if (parse->limitOffset || parse->limitCount)
+	{
+		result_plan = (Plan *) make_limit(tlist, result_plan,
+										  parse->limitOffset,
+										  parse->limitCount);
+	}
+
 	return result_plan;
 }
 

src/backend/optimizer/plan/setrefs.c

@@ -9,7 +9,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/optimizer/plan/setrefs.c,v 1.67 2000/10/05 19:11:29 tgl Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/optimizer/plan/setrefs.c,v 1.68 2000/10/26 21:36:09 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -139,6 +139,7 @@ set_plan_references(Plan *plan)
 		case T_Sort:
 		case T_Unique:
 		case T_SetOp:
+		case T_Limit:
 		case T_Hash:
 
 			/*

src/backend/optimizer/plan/subselect.c

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/optimizer/plan/subselect.c,v 1.43 2000/10/05 19:11:29 tgl Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/optimizer/plan/subselect.c,v 1.44 2000/10/26 21:36:09 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -657,6 +657,7 @@ SS_finalize_plan(Plan *plan)
 		case T_Sort:
 		case T_Unique:
 		case T_SetOp:
+		case T_Limit:
 		case T_Group:
 			break;