1 files changed, 80 insertions, 0 deletions
diff --git a/src/backend/executor/execUtils.c b/src/backend/executor/execUtils.c
index e8c06c76056..876439835a3 100644
--- a/src/backend/executor/execUtils.c
+++ b/src/backend/executor/execUtils.c
@@ -56,6 +56,7 @@
 #include "utils/typcache.h"
 
 
+static bool tlist_matches_tupdesc(PlanState *ps, List *tlist, Index varno, TupleDesc tupdesc);
 static void ShutdownExprContext(ExprContext *econtext, bool isCommit);
 
 
@@ -504,6 +505,85 @@ ExecAssignProjectionInfo(PlanState *planstate,
 
 
 /* ----------------
+ *		ExecConditionalAssignProjectionInfo
+ *
+ * as ExecAssignProjectionInfo, but store NULL rather than building projection
+ * info if no projection is required
+ * ----------------
+ */
+void
+ExecConditionalAssignProjectionInfo(PlanState *planstate, TupleDesc inputDesc,
+									Index varno)
+{
+	if (tlist_matches_tupdesc(planstate,
+							  planstate->plan->targetlist,
+							  varno,
+							  inputDesc))
+		planstate->ps_ProjInfo = NULL;
+	else
+		ExecAssignProjectionInfo(planstate, inputDesc);
+}
+
+static bool
+tlist_matches_tupdesc(PlanState *ps, List *tlist, Index varno, TupleDesc tupdesc)
+{
+	int			numattrs = tupdesc->natts;
+	int			attrno;
+	bool		hasoid;
+	ListCell   *tlist_item = list_head(tlist);
+
+	/* Check the tlist attributes */
+	for (attrno = 1; attrno <= numattrs; attrno++)
+	{
+		Form_pg_attribute att_tup = TupleDescAttr(tupdesc, attrno - 1);
+		Var		   *var;
+
+		if (tlist_item == NULL)
+			return false;		/* tlist too short */
+		var = (Var *) ((TargetEntry *) lfirst(tlist_item))->expr;
+		if (!var || !IsA(var, Var))
+			return false;		/* tlist item not a Var */
+		/* if these Asserts fail, planner messed up */
+		Assert(var->varno == varno);
+		Assert(var->varlevelsup == 0);
+		if (var->varattno != attrno)
+			return false;		/* out of order */
+		if (att_tup->attisdropped)
+			return false;		/* table contains dropped columns */
+
+		/*
+		 * Note: usually the Var's type should match the tupdesc exactly, but
+		 * in situations involving unions of columns that have different
+		 * typmods, the Var may have come from above the union and hence have
+		 * typmod -1.  This is a legitimate situation since the Var still
+		 * describes the column, just not as exactly as the tupdesc does. We
+		 * could change the planner to prevent it, but it'd then insert
+		 * projection steps just to convert from specific typmod to typmod -1,
+		 * which is pretty silly.
+		 */
+		if (var->vartype != att_tup->atttypid ||
+			(var->vartypmod != att_tup->atttypmod &&
+			 var->vartypmod != -1))
+			return false;		/* type mismatch */
+
+		tlist_item = lnext(tlist_item);
+	}
+
+	if (tlist_item)
+		return false;			/* tlist too long */
+
+	/*
+	 * If the plan context requires a particular hasoid setting, then that has
+	 * to match, too.
+	 */
+	if (ExecContextForcesOids(ps, &hasoid) &&
+		hasoid != tupdesc->tdhasoid)
+		return false;
+
+	return true;
+}
+
+/* ----------------
  *		ExecFreeExprContext
  *
  * A plan node's ExprContext should be freed explicitly during executor