From f144f73242acef574bc27a4c70e809a64806e4a4 Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Thu, 11 Feb 2016 17:52:03 -0500
Subject: [PATCH] Refactor check_functional_grouping() to use
 get_primary_key_attnos().

If we ever get around to allowing functional dependency to be proven
from other things besides simple primary keys, this code will need to
be rethought, but that was true anyway.  In the meantime, we might as
well not have two very-similar routines for scanning pg_constraint.

David Rowley, reviewed by Julien Rouhaud
---
 src/backend/catalog/pg_constraint.c | 110 +++++++---------------------
 1 file changed, 26 insertions(+), 84 deletions(-)

diff --git a/src/backend/catalog/pg_constraint.c b/src/backend/catalog/pg_constraint.c
index 74007856f3..8fabe6899f 100644
--- a/src/backend/catalog/pg_constraint.c
+++ b/src/backend/catalog/pg_constraint.c
@@ -986,93 +986,35 @@ check_functional_grouping(Oid relid,
 						  List *grouping_columns,
 						  List **constraintDeps)
 {
-	bool		result = false;
-	Relation	pg_constraint;
-	HeapTuple	tuple;
-	SysScanDesc scan;
-	ScanKeyData skey[1];
-
-	/* Scan pg_constraint for constraints of the target rel */
-	pg_constraint = heap_open(ConstraintRelationId, AccessShareLock);
-
-	ScanKeyInit(&skey[0],
-				Anum_pg_constraint_conrelid,
-				BTEqualStrategyNumber, F_OIDEQ,
-				ObjectIdGetDatum(relid));
-
-	scan = systable_beginscan(pg_constraint, ConstraintRelidIndexId, true,
-							  NULL, 1, skey);
-
-	while (HeapTupleIsValid(tuple = systable_getnext(scan)))
+	Bitmapset  *pkattnos;
+	Bitmapset  *groupbyattnos;
+	Oid			constraintOid;
+	ListCell   *gl;
+
+	/* If the rel has no PK, then we can't prove functional dependency */
+	pkattnos = get_primary_key_attnos(relid, false, &constraintOid);
+	if (pkattnos == NULL)
+		return false;
+
+	/* Identify all the rel's columns that appear in grouping_columns */
+	groupbyattnos = NULL;
+	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;
+		Var		   *gvar = (Var *) lfirst(gl);
 
-		/* 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;
-
-		/* 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);
+	if (bms_is_subset(pkattnos, groupbyattnos))
+	{
+		/* The PK is a subset of grouping_columns, so we win */
+		*constraintDeps = lappend_oid(*constraintDeps, constraintOid);
+		return true;
+	}
 
-	return result;
+	return false;
 }
-- 
2.40.0