diff --git a/src/backend/catalog/pg_constraint.c b/src/backend/catalog/pg_constraint.c
index 3e70d07..af160d5 100644
--- a/src/backend/catalog/pg_constraint.c
+++ b/src/backend/catalog/pg_constraint.c
@@ -976,93 +976,32 @@ check_functional_grouping(Oid relid,
 						  List *grouping_columns,
 						  List **constraintDeps)
 {
-	bool		result = false;
-	Relation	pg_constraint;
-	HeapTuple	tuple;
-	SysScanDesc scan;
-	ScanKeyData skey[1];
+	Bitmapset	   *pkattnos;
+	Bitmapset	   *groupbyattnos = NULL;
+	Oid				constraintOid;
+	ListCell	   *gl;
 
-	/* Scan pg_constraint for constraints of the target rel */
-	pg_constraint = heap_open(ConstraintRelationId, AccessShareLock);
+	pkattnos = get_primary_key_attnos(relid, false, &constraintOid);
 
-	ScanKeyInit(&skey[0],
-				Anum_pg_constraint_conrelid,
-				BTEqualStrategyNumber, F_OIDEQ,
-				ObjectIdGetDatum(relid));
+	/* if the rel has no PK, then we can't prove functional dependency */
+	if (pkattnos == NULL)
+		return false;
 
-	scan = systable_beginscan(pg_constraint, ConstraintRelidIndexId, true,
-							  NULL, 1, skey);
-
-	while (HeapTupleIsValid(tuple = systable_getnext(scan)))
+	foreach(gl, grouping_columns)
 	{
-		Form_pg_constraint con = (Form_pg_constraint) GETSTRUCT(tuple);
-		Datum		adatum;
-		bool		isNull;
-		ArrayType  *arr;
-		int16	   *attnums;
-		int			numkeys;
-		int			i;
-		bool		found_col;
-
-		/* Only PK constraints are of interest for now, see comment above */
-		if (con->contype != CONSTRAINT_PRIMARY)
-			continue;
-		/* Constraint must be non-deferrable */
-		if (con->condeferrable)
-			continue;
+		Var		   *gvar = (Var *) lfirst(gl);
 
-		/* Extract the conkey array, ie, attnums of PK's columns */
-		adatum = heap_getattr(tuple, Anum_pg_constraint_conkey,
-							  RelationGetDescr(pg_constraint), &isNull);
-		if (isNull)
-			elog(ERROR, "null conkey for constraint %u",
-				 HeapTupleGetOid(tuple));
-		arr = DatumGetArrayTypeP(adatum);		/* ensure not toasted */
-		numkeys = ARR_DIMS(arr)[0];
-		if (ARR_NDIM(arr) != 1 ||
-			numkeys < 0 ||
-			ARR_HASNULL(arr) ||
-			ARR_ELEMTYPE(arr) != INT2OID)
-			elog(ERROR, "conkey is not a 1-D smallint array");
-		attnums = (int16 *) ARR_DATA_PTR(arr);
-
-		found_col = false;
-		for (i = 0; i < numkeys; i++)
-		{
-			AttrNumber	attnum = attnums[i];
-			ListCell   *gl;
-
-			found_col = false;
-			foreach(gl, grouping_columns)
-			{
-				Var		   *gvar = (Var *) lfirst(gl);
-
-				if (IsA(gvar, Var) &&
-					gvar->varno == varno &&
-					gvar->varlevelsup == varlevelsup &&
-					gvar->varattno == attnum)
-				{
-					found_col = true;
-					break;
-				}
-			}
-			if (!found_col)
-				break;
-		}
-
-		if (found_col)
-		{
-			/* The PK is a subset of grouping_columns, so we win */
-			*constraintDeps = lappend_oid(*constraintDeps,
-										  HeapTupleGetOid(tuple));
-			result = true;
-			break;
-		}
+		if (IsA(gvar, Var) &&
+			gvar->varno == varno &&
+			gvar->varlevelsup == varlevelsup)
+			groupbyattnos = bms_add_member(groupbyattnos, gvar->varattno -
+										   FirstLowInvalidHeapAttributeNumber);
 	}
 
-	systable_endscan(scan);
-
-	heap_close(pg_constraint, AccessShareLock);
-
-	return result;
+	if (bms_is_subset(pkattnos, groupbyattnos))
+	{
+		*constraintDeps = lappend_oid(*constraintDeps, constraintOid);
+		return true;
+	}
+	return false;
 }