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diff --git a/src/backend/executor/nodeResult.c b/src/backend/executor/nodeResult.c
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+/*-------------------------------------------------------------------------
+ *
+ * nodeResult.c
+ *	  support for constant nodes needing special code.
+ *
+ * DESCRIPTION
+ *
+ *		Result nodes are used in queries where no relations are scanned.
+ *		Examples of such queries are:
+ *
+ *				select 1 * 2
+ *
+ *				insert into emp values ('mike', 15000)
+ *
+ *		(Remember that in an INSERT or UPDATE, we need a plan tree that
+ *		generates the new rows.)
+ *
+ *		Result nodes are also used to optimise queries with constant
+ *		qualifications (ie, quals that do not depend on the scanned data),
+ *		such as:
+ *
+ *				select * from emp where 2 > 1
+ *
+ *		In this case, the plan generated is
+ *
+ *						Result	(with 2 > 1 qual)
+ *						/
+ *				   SeqScan (emp.*)
+ *
+ *		At runtime, the Result node evaluates the constant qual once,
+ *		which is shown by EXPLAIN as a One-Time Filter.  If it's
+ *		false, we can return an empty result set without running the
+ *		controlled plan at all.  If it's true, we run the controlled
+ *		plan normally and pass back the results.
+ *
+ *
+ * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * IDENTIFICATION
+ *	  src/backend/executor/nodeResult.c
+ *
+ *-------------------------------------------------------------------------
+ */
+
+#include "postgres.h"
+
+#include "executor/executor.h"
+#include "executor/nodeResult.h"
+#include "miscadmin.h"
+#include "utils/memutils.h"
+
+
+/* ----------------------------------------------------------------
+ *		ExecResult(node)
+ *
+ *		returns the tuples from the outer plan which satisfy the
+ *		qualification clause.  Since result nodes with right
+ *		subtrees are never planned, we ignore the right subtree
+ *		entirely (for now).. -cim 10/7/89
+ *
+ *		The qualification containing only constant clauses are
+ *		checked first before any processing is done. It always returns
+ *		'nil' if the constant qualification is not satisfied.
+ * ----------------------------------------------------------------
+ */
+static TupleTableSlot *
+ExecResult(PlanState *pstate)
+{
+	ResultState *node = castNode(ResultState, pstate);
+	TupleTableSlot *outerTupleSlot;
+	PlanState  *outerPlan;
+	ExprContext *econtext;
+
+	CHECK_FOR_INTERRUPTS();
+
+	econtext = node->ps.ps_ExprContext;
+
+	/*
+	 * check constant qualifications like (2 > 1), if not already done
+	 */
+	if (node->rs_checkqual)
+	{
+		bool		qualResult = ExecQual(node->resconstantqual, econtext);
+
+		node->rs_checkqual = false;
+		if (!qualResult)
+		{
+			node->rs_done = true;
+			return NULL;
+		}
+	}
+
+	/*
+	 * Reset per-tuple memory context to free any expression evaluation
+	 * storage allocated in the previous tuple cycle.
+	 */
+	ResetExprContext(econtext);
+
+	/*
+	 * if rs_done is true then it means that we were asked to return a
+	 * constant tuple and we already did the last time ExecResult() was
+	 * called, OR that we failed the constant qual check. Either way, now we
+	 * are through.
+	 */
+	if (!node->rs_done)
+	{
+		outerPlan = outerPlanState(node);
+
+		if (outerPlan != NULL)
+		{
+			/*
+			 * retrieve tuples from the outer plan until there are no more.
+			 */
+			outerTupleSlot = ExecProcNode(outerPlan);
+
+			if (TupIsNull(outerTupleSlot))
+				return NULL;
+
+			/*
+			 * prepare to compute projection expressions, which will expect to
+			 * access the input tuples as varno OUTER.
+			 */
+			econtext->ecxt_outertuple = outerTupleSlot;
+		}
+		else
+		{
+			/*
+			 * if we don't have an outer plan, then we are just generating the
+			 * results from a constant target list.  Do it only once.
+			 */
+			node->rs_done = true;
+		}
+
+		/* form the result tuple using ExecProject(), and return it */
+		return ExecProject(node->ps.ps_ProjInfo);
+	}
+
+	return NULL;
+}
+
+/* ----------------------------------------------------------------
+ *		ExecResultMarkPos
+ * ----------------------------------------------------------------
+ */
+void
+ExecResultMarkPos(ResultState *node)
+{
+	PlanState  *outerPlan = outerPlanState(node);
+
+	if (outerPlan != NULL)
+		ExecMarkPos(outerPlan);
+	else
+		elog(DEBUG2, "Result nodes do not support mark/restore");
+}
+
+/* ----------------------------------------------------------------
+ *		ExecResultRestrPos
+ * ----------------------------------------------------------------
+ */
+void
+ExecResultRestrPos(ResultState *node)
+{
+	PlanState  *outerPlan = outerPlanState(node);
+
+	if (outerPlan != NULL)
+		ExecRestrPos(outerPlan);
+	else
+		elog(ERROR, "Result nodes do not support mark/restore");
+}
+
+/* ----------------------------------------------------------------
+ *		ExecInitResult
+ *
+ *		Creates the run-time state information for the result node
+ *		produced by the planner and initializes outer relations
+ *		(child nodes).
+ * ----------------------------------------------------------------
+ */
+ResultState *
+ExecInitResult(Result *node, EState *estate, int eflags)
+{
+	ResultState *resstate;
+
+	/* check for unsupported flags */
+	Assert(!(eflags & (EXEC_FLAG_MARK | EXEC_FLAG_BACKWARD)) ||
+		   outerPlan(node) != NULL);
+
+	/*
+	 * create state structure
+	 */
+	resstate = makeNode(ResultState);
+	resstate->ps.plan = (Plan *) node;
+	resstate->ps.state = estate;
+	resstate->ps.ExecProcNode = ExecResult;
+
+	resstate->rs_done = false;
+	resstate->rs_checkqual = (node->resconstantqual == NULL) ? false : true;
+
+	/*
+	 * Miscellaneous initialization
+	 *
+	 * create expression context for node
+	 */
+	ExecAssignExprContext(estate, &resstate->ps);
+
+	/*
+	 * initialize child nodes
+	 */
+	outerPlanState(resstate) = ExecInitNode(outerPlan(node), estate, eflags);
+
+	/*
+	 * we don't use inner plan
+	 */
+	Assert(innerPlan(node) == NULL);
+
+	/*
+	 * Initialize result slot, type and projection.
+	 */
+	ExecInitResultTupleSlotTL(&resstate->ps, &TTSOpsVirtual);
+	ExecAssignProjectionInfo(&resstate->ps, NULL);
+
+	/*
+	 * initialize child expressions
+	 */
+	resstate->ps.qual =
+		ExecInitQual(node->plan.qual, (PlanState *) resstate);
+	resstate->resconstantqual =
+		ExecInitQual((List *) node->resconstantqual, (PlanState *) resstate);
+
+	return resstate;
+}
+
+/* ----------------------------------------------------------------
+ *		ExecEndResult
+ *
+ *		frees up storage allocated through C routines
+ * ----------------------------------------------------------------
+ */
+void
+ExecEndResult(ResultState *node)
+{
+	/*
+	 * Free the exprcontext
+	 */
+	ExecFreeExprContext(&node->ps);
+
+	/*
+	 * clean out the tuple table
+	 */
+	ExecClearTuple(node->ps.ps_ResultTupleSlot);
+
+	/*
+	 * shut down subplans
+	 */
+	ExecEndNode(outerPlanState(node));
+}
+
+void
+ExecReScanResult(ResultState *node)
+{
+	node->rs_done = false;
+	node->rs_checkqual = (node->resconstantqual == NULL) ? false : true;
+
+	/*
+	 * If chgParam of subnode is not null then plan will be re-scanned by
+	 * first ExecProcNode.
+	 */
+	if (node->ps.lefttree &&
+		node->ps.lefttree->chgParam == NULL)
+		ExecReScan(node->ps.lefttree);
+}