Don't reject ROW_MARK_REFERENCE rowmarks for materialized views.

We should allow this so that matviews can be referenced in UPDATE/DELETE
statements in READ COMMITTED isolation level.  The requirement for that
is that a re-fetch by TID will see the same row version the query saw
earlier, which is true of matviews, so there's no reason for the
restriction.  Per bug #9398.

Michael Paquier, after a suggestion by me

src/backend/executor/execMain.c

@@ -1102,14 +1102,15 @@ CheckValidRowMarkRel(Relation rel, RowMarkType markType)
 							RelationGetRelationName(rel))));
 			break;
 		case RELKIND_MATVIEW:
-			/* Should not get here */
-			ereport(ERROR,
-					(errcode(ERRCODE_WRONG_OBJECT_TYPE),
-					 errmsg("cannot lock rows in materialized view \"%s\"",
-							RelationGetRelationName(rel))));
+			/* Allow referencing a matview, but not actual locking clauses */
+			if (markType != ROW_MARK_REFERENCE)
+				ereport(ERROR,
+						(errcode(ERRCODE_WRONG_OBJECT_TYPE),
+					   errmsg("cannot lock rows in materialized view \"%s\"",
+							  RelationGetRelationName(rel))));
 			break;
 		case RELKIND_FOREIGN_TABLE:
-			/* Should not get here */
+			/* Should not get here; planner should have used ROW_MARK_COPY */
 			ereport(ERROR,
 					(errcode(ERRCODE_WRONG_OBJECT_TYPE),
 					 errmsg("cannot lock rows in foreign table \"%s\"",

src/test/regress/expected/matview.out

@@ -476,3 +476,29 @@ SELECT * FROM mv_v;
 
 DROP TABLE v CASCADE;
 NOTICE:  drop cascades to materialized view mv_v
+-- make sure that matview rows can be referenced as source rows (bug #9398)
+CREATE TABLE v AS SELECT generate_series(1,10) AS a;
+CREATE MATERIALIZED VIEW mv_v AS SELECT a FROM v WHERE a <= 5;
+DELETE FROM v WHERE EXISTS ( SELECT * FROM mv_v WHERE mv_v.a = v.a );
+SELECT * FROM v;
+ a  
+----
+  6
+  7
+  8
+  9
+ 10
+(5 rows)
+
+SELECT * FROM mv_v;
+ a 
+---
+ 1
+ 2
+ 3
+ 4
+ 5
+(5 rows)
+
+DROP TABLE v CASCADE;
+NOTICE:  drop cascades to materialized view mv_v

src/test/regress/sql/matview.sql

@@ -186,3 +186,11 @@ REFRESH MATERIALIZED VIEW CONCURRENTLY mv_v;
 SELECT * FROM v;
 SELECT * FROM mv_v;
 DROP TABLE v CASCADE;
+
+-- make sure that matview rows can be referenced as source rows (bug #9398)
+CREATE TABLE v AS SELECT generate_series(1,10) AS a;
+CREATE MATERIALIZED VIEW mv_v AS SELECT a FROM v WHERE a <= 5;
+DELETE FROM v WHERE EXISTS ( SELECT * FROM mv_v WHERE mv_v.a = v.a );
+SELECT * FROM v;
+SELECT * FROM mv_v;
+DROP TABLE v CASCADE;