Fix LATERAL references to target table of UPDATE/DELETE.

I failed to think much about UPDATE/DELETE when implementing LATERAL :-(.
The implemented behavior ended up being that subqueries in the FROM or
USING clause (respectively) could access the update/delete target table as
though it were a lateral reference; which seems fine if they said LATERAL,
but certainly ought to draw an error if they didn't.  Fix it so you get a
suitable error when you omit LATERAL.  Per report from Emre Hasegeli.

src/backend/parser/analyze.c

@@ -342,6 +342,7 @@ static Query *
 transformDeleteStmt(ParseState *pstate, DeleteStmt *stmt)
 {
 	Query	   *qry = makeNode(Query);
+	ParseNamespaceItem *nsitem;
 	Node	   *qual;
 
 	qry->commandType = CMD_DELETE;
@@ -360,8 +361,15 @@ transformDeleteStmt(ParseState *pstate, DeleteStmt *stmt)
 										 true,
 										 ACL_DELETE);
 
+	/* grab the namespace item made by setTargetTable */
+	nsitem = (ParseNamespaceItem *) llast(pstate->p_namespace);
+
+	/* there's no DISTINCT in DELETE */
 	qry->distinctClause = NIL;
 
+	/* subqueries in USING can see the result relation only via LATERAL */
+	nsitem->p_lateral_only = true;
+
 	/*
 	 * The USING clause is non-standard SQL syntax, and is equivalent in
 	 * functionality to the FROM list that can be specified for UPDATE. The
@@ -370,6 +378,9 @@ transformDeleteStmt(ParseState *pstate, DeleteStmt *stmt)
 	 */
 	transformFromClause(pstate, stmt->usingClause);
 
+	/* remaining clauses can see the result relation normally */
+	nsitem->p_lateral_only = false;
+
 	qual = transformWhereClause(pstate, stmt->whereClause,
 								EXPR_KIND_WHERE, "WHERE");
 
@@ -1889,6 +1900,7 @@ static Query *
 transformUpdateStmt(ParseState *pstate, UpdateStmt *stmt)
 {
 	Query	   *qry = makeNode(Query);
+	ParseNamespaceItem *nsitem;
 	RangeTblEntry *target_rte;
 	Node	   *qual;
 	ListCell   *origTargetList;
@@ -1910,12 +1922,21 @@ transformUpdateStmt(ParseState *pstate, UpdateStmt *stmt)
 										 true,
 										 ACL_UPDATE);
 
+	/* grab the namespace item made by setTargetTable */
+	nsitem = (ParseNamespaceItem *) llast(pstate->p_namespace);
+
+	/* subqueries in FROM can see the result relation only via LATERAL */
+	nsitem->p_lateral_only = true;
+
 	/*
 	 * the FROM clause is non-standard SQL syntax. We used to be able to do
 	 * this with REPLACE in POSTQUEL so we keep the feature.
 	 */
 	transformFromClause(pstate, stmt->fromClause);
 
+	/* remaining clauses can see the result relation normally */
+	nsitem->p_lateral_only = false;
+
 	qry->targetList = transformTargetList(pstate, stmt->targetList,
 										  EXPR_KIND_UPDATE_SOURCE);
 

src/backend/parser/parse_clause.c

@@ -204,6 +204,10 @@ setTargetTable(ParseState *pstate, RangeVar *relation,
 
 	/*
 	 * If UPDATE/DELETE, add table to joinlist and namespace.
+	 *
+	 * Note: some callers know that they can find the new ParseNamespaceItem
+	 * at the end of the pstate->p_namespace list.  This is a bit ugly but not
+	 * worth complicating this function's signature for.
 	 */
 	if (alsoSource)
 		addRTEtoQuery(pstate, rte, true, true, true);

src/backend/parser/parse_relation.c

@@ -1730,6 +1730,10 @@ isLockedRefname(ParseState *pstate, const char *refname)
  * and/or namespace list.  (We assume caller has checked for any
  * namespace conflicts.)  The RTE is always marked as unconditionally
  * visible, that is, not LATERAL-only.
+ *
+ * Note: some callers know that they can find the new ParseNamespaceItem
+ * at the end of the pstate->p_namespace list.  This is a bit ugly but not
+ * worth complicating this function's signature for.
  */
 void
 addRTEtoQuery(ParseState *pstate, RangeTblEntry *rte,

src/test/regress/expected/join.out

@@ -4103,3 +4103,51 @@ select 1 from tenk1 a, lateral (select max(a.unique1) from int4_tbl b) ss;
 ERROR:  aggregate functions are not allowed in FROM clause of their own query level
 LINE 1: select 1 from tenk1 a, lateral (select max(a.unique1) from i...
                                                ^
+-- check behavior of LATERAL in UPDATE/DELETE
+create temp table xx1 as select f1 as x1, -f1 as x2 from int4_tbl;
+select * from xx1;
+     x1      |     x2      
+-------------+-------------
+           0 |           0
+      123456 |     -123456
+     -123456 |      123456
+  2147483647 | -2147483647
+ -2147483647 |  2147483647
+(5 rows)
+
+-- error, can't do this without LATERAL:
+update xx1 set x2 = f1 from (select * from int4_tbl where f1 = x1) ss;
+ERROR:  column "x1" does not exist
+LINE 1: ... set x2 = f1 from (select * from int4_tbl where f1 = x1) ss;
+                                                                ^
+HINT:  There is a column named "x1" in table "xx1", but it cannot be referenced from this part of the query.
+update xx1 set x2 = f1 from (select * from int4_tbl where f1 = xx1.x1) ss;
+ERROR:  invalid reference to FROM-clause entry for table "xx1"
+LINE 1: ...t x2 = f1 from (select * from int4_tbl where f1 = xx1.x1) ss...
+                                                             ^
+HINT:  There is an entry for table "xx1", but it cannot be referenced from this part of the query.
+-- OK:
+update xx1 set x2 = f1 from lateral (select * from int4_tbl where f1 = x1) ss;
+select * from xx1;
+     x1      |     x2      
+-------------+-------------
+           0 |           0
+      123456 |      123456
+     -123456 |     -123456
+  2147483647 |  2147483647
+ -2147483647 | -2147483647
+(5 rows)
+
+-- error:
+delete from xx1 using (select * from int4_tbl where f1 = x1) ss;
+ERROR:  column "x1" does not exist
+LINE 1: ...te from xx1 using (select * from int4_tbl where f1 = x1) ss;
+                                                                ^
+HINT:  There is a column named "x1" in table "xx1", but it cannot be referenced from this part of the query.
+-- OK:
+delete from xx1 using lateral (select * from int4_tbl where f1 = x1) ss;
+select * from xx1;
+ x1 | x2 
+----+----
+(0 rows)
+

src/test/regress/sql/join.sql

@@ -1147,3 +1147,21 @@ select * from
   int8_tbl x cross join (int4_tbl x cross join lateral (select x.f1) ss);
 -- LATERAL can be used to put an aggregate into the FROM clause of its query
 select 1 from tenk1 a, lateral (select max(a.unique1) from int4_tbl b) ss;
+
+-- check behavior of LATERAL in UPDATE/DELETE
+
+create temp table xx1 as select f1 as x1, -f1 as x2 from int4_tbl;
+select * from xx1;
+
+-- error, can't do this without LATERAL:
+update xx1 set x2 = f1 from (select * from int4_tbl where f1 = x1) ss;
+update xx1 set x2 = f1 from (select * from int4_tbl where f1 = xx1.x1) ss;
+-- OK:
+update xx1 set x2 = f1 from lateral (select * from int4_tbl where f1 = x1) ss;
+select * from xx1;
+
+-- error:
+delete from xx1 using (select * from int4_tbl where f1 = x1) ss;
+-- OK:
+delete from xx1 using lateral (select * from int4_tbl where f1 = x1) ss;
+select * from xx1;