2 files changed, 104 insertions, 3 deletions

diff --git a/src/backend/executor/execQual.c b/src/backend/executor/execQual.c
index 7761485d7c1..57b2df9c00e 100644
--- a/src/backend/executor/execQual.c
+++ b/src/backend/executor/execQual.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/executor/execQual.c,v 1.231 2008/05/15 00:17:39 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/executor/execQual.c,v 1.232 2008/08/22 00:16:03 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -3957,6 +3957,19 @@ ExecInitExpr(Expr *node, PlanState *parent)
 				state = (ExprState *) sstate;
 			}
 			break;
+		case T_AlternativeSubPlan:
+			{
+				AlternativeSubPlan *asplan = (AlternativeSubPlan *) node;
+				AlternativeSubPlanState *asstate;
+
+				if (!parent)
+					elog(ERROR, "AlternativeSubPlan found with no parent plan");
+
+				asstate = ExecInitAlternativeSubPlan(asplan, parent);
+
+				state = (ExprState *) asstate;
+			}
+			break;
 		case T_FieldSelect:
 			{
 				FieldSelect *fselect = (FieldSelect *) node;
diff --git a/src/backend/executor/nodeSubplan.c b/src/backend/executor/nodeSubplan.c
index 0c9ec82b01d..3ebb045f922 100644
--- a/src/backend/executor/nodeSubplan.c
+++ b/src/backend/executor/nodeSubplan.c
@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/executor/nodeSubplan.c,v 1.93 2008/05/12 00:00:49 alvherre Exp $
+ *	  $PostgreSQL: pgsql/src/backend/executor/nodeSubplan.c,v 1.94 2008/08/22 00:16:03 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -29,6 +29,14 @@
 #include "utils/memutils.h"
 
 
+static Datum ExecSubPlan(SubPlanState *node,
+			ExprContext *econtext,
+			bool *isNull,
+			ExprDoneCond *isDone);
+static Datum ExecAlternativeSubPlan(AlternativeSubPlanState *node,
+			ExprContext *econtext,
+			bool *isNull,
+			ExprDoneCond *isDone);
 static Datum ExecHashSubPlan(SubPlanState *node,
 				ExprContext *econtext,
 				bool *isNull);
@@ -45,7 +53,7 @@ static bool slotNoNulls(TupleTableSlot *slot);
  *		ExecSubPlan
  * ----------------------------------------------------------------
  */
-Datum
+static Datum
 ExecSubPlan(SubPlanState *node,
 			ExprContext *econtext,
 			bool *isNull,
@@ -1066,3 +1074,83 @@ ExecReScanSetParamPlan(SubPlanState *node, PlanState *parent)
 		parent->chgParam = bms_add_member(parent->chgParam, paramid);
 	}
 }
+
+
+/*
+ * ExecInitAlternativeSubPlan
+ *
+ * Initialize for execution of one of a set of alternative subplans.
+ */
+AlternativeSubPlanState *
+ExecInitAlternativeSubPlan(AlternativeSubPlan *asplan, PlanState *parent)
+{
+	AlternativeSubPlanState *asstate = makeNode(AlternativeSubPlanState);
+	double		num_calls;
+	SubPlan	   *subplan1;
+	SubPlan	   *subplan2;
+	Cost		cost1;
+	Cost		cost2;
+
+	asstate->xprstate.evalfunc = (ExprStateEvalFunc) ExecAlternativeSubPlan;
+	asstate->xprstate.expr = (Expr *) asplan;
+
+	/*
+	 * Initialize subplans.  (Can we get away with only initializing the
+	 * one we're going to use?)
+	 */
+	asstate->subplans = (List *) ExecInitExpr((Expr *) asplan->subplans,
+											  parent);
+
+	/*
+	 * Select the one to be used.  For this, we need an estimate of the
+	 * number of executions of the subplan.  We use the number of output
+	 * rows expected from the parent plan node.  This is a good estimate
+	 * if we are in the parent's targetlist, and an underestimate (but
+	 * probably not by more than a factor of 2) if we are in the qual.
+	 */
+	num_calls = parent->plan->plan_rows;
+
+	/*
+	 * The planner saved enough info so that we don't have to work very hard
+	 * to estimate the total cost, given the number-of-calls estimate.
+	 */
+	Assert(list_length(asplan->subplans) == 2);
+	subplan1 = (SubPlan *) linitial(asplan->subplans);
+	subplan2 = (SubPlan *) lsecond(asplan->subplans);
+
+	cost1 = subplan1->startup_cost + num_calls * subplan1->per_call_cost;
+	cost2 = subplan2->startup_cost + num_calls * subplan2->per_call_cost;
+
+	if (cost1 < cost2)
+		asstate->active = 0;
+	else
+		asstate->active = 1;
+
+	return asstate;
+}
+
+/*
+ * ExecAlternativeSubPlan
+ *
+ * Execute one of a set of alternative subplans.
+ *
+ * Note: in future we might consider changing to different subplans on the
+ * fly, in case the original rowcount estimate turns out to be way off.
+ */
+static Datum
+ExecAlternativeSubPlan(AlternativeSubPlanState *node,
+					   ExprContext *econtext,
+					   bool *isNull,
+					   ExprDoneCond *isDone)
+{
+	/* Just pass control to the active subplan */
+	SubPlanState   *activesp = (SubPlanState *) list_nth(node->subplans,
+														 node->active);
+
+	Assert(IsA(activesp, SubPlanState));
+
+	return ExecSubPlan(activesp,
+					   econtext,
+					   isNull,
+					   isDone);
+}