Fix rewriter to set hasModifyingCTE correctly on rewritten queries.

If we copy data-modifying CTEs from the original query to a replacement
query (from a DO INSTEAD rule), we must set hasModifyingCTE properly
in the replacement query.  Failure to do this can cause various
unpleasantness, such as unsafe usage of parallel plans.  The code also
neglected to propagate hasRecursive, though that's only cosmetic at
the moment.

A difficulty arises if the rule action is an INSERT...SELECT.  We
attach the original query's RTEs and CTEs to the sub-SELECT Query, but
data-modifying CTEs are only allowed to appear in the topmost Query.
For the moment, throw an error in such cases.  It would probably be
possible to avoid this error by attaching the CTEs to the top INSERT
Query instead; but that would require a bunch of new code to adjust
ctelevelsup references.  Given the narrowness of the use-case, and
the need to back-patch this fix, it does not seem worth the trouble
for now.  We can revisit this if we get field complaints.

Per report from Greg Nancarrow.  Back-patch to all supported branches.
(The test case added here does not fail before v10, but there are
plenty of places checking top-level hasModifyingCTE in 9.6, so I have
no doubt that this code change is necessary there too.)

Greg Nancarrow and Tom Lane

Discussion: https://postgr.es/m/CAJcOf-f68DT=26YAMz_i0+Au3TcLO5oiHY5=fL6Sfuits6r+_w@mail.gmail.com
Discussion: https://postgr.es/m/CAJcOf-fAdj=nDKMsRhQzndm-O13NY4dL6xGcEvdX5Xvbbi0V7g@mail.gmail.com

diff --git a/src/backend/rewrite/rewriteHandler.c b/src/backend/rewrite/rewriteHandler.c
index 14893ed5cd824b59220661ed6fe26421637b53f5..bb2669b5df8f1d965aaae5c9a292bc1769a77806 100644 (file)
--- a/src/backend/rewrite/rewriteHandler.c
+++ b/src/backend/rewrite/rewriteHandler.c
@@ -530,6 +530,9 @@ rewriteRuleAction(Query *parsetree,
                 *
                 * This could possibly be fixed by using some sort of internally
                 * generated ID, instead of names, to link CTE RTEs to their CTEs.
+                * However, decompiling the results would be quite confusing; note the
+                * merge of hasRecursive flags below, which could change the apparent
+                * semantics of such redundantly-named CTEs.
                 */
                foreach(lc, parsetree->cteList)
                {
@@ -551,6 +554,26 @@ rewriteRuleAction(Query *parsetree,
                /* OK, it's safe to combine the CTE lists */
                sub_action->cteList = list_concat(sub_action->cteList,
                                                                                  copyObject(parsetree->cteList));
+               /* ... and don't forget about the associated flags */
+               sub_action->hasRecursive |= parsetree->hasRecursive;
+               sub_action->hasModifyingCTE |= parsetree->hasModifyingCTE;
+
+               /*
+                * If rule_action is different from sub_action (i.e., the rule action
+                * is an INSERT...SELECT), then we might have just added some
+                * data-modifying CTEs that are not at the top query level.  This is
+                * disallowed by the parser and we mustn't generate such trees here
+                * either, so throw an error.
+                *
+                * Conceivably such cases could be supported by attaching the original
+                * query's CTEs to rule_action not sub_action.  But to do that, we'd
+                * have to increment ctelevelsup in RTEs and SubLinks copied from the
+                * original query.  For now, it doesn't seem worth the trouble.
+                */
+               if (sub_action->hasModifyingCTE && rule_action != sub_action)
+                       ereport(ERROR,
+                                       (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+                                        errmsg("INSERT...SELECT rule actions are not supported for queries having data-modifying statements in WITH")));
        }
 
        /*

diff --git a/src/test/regress/expected/with.out b/src/test/regress/expected/with.out
index 9a99bd64194672cf5287dc34205bb3adb69dcd1c..e4924e786be9f5cc18a99a3bf189e0ca72761a41 100644 (file)
--- a/src/test/regress/expected/with.out
+++ b/src/test/regress/expected/with.out
@@ -1715,7 +1715,7 @@ SELECT * FROM bug6051;
 CREATE TEMP TABLE bug6051_2 (i int);
 CREATE RULE bug6051_ins AS ON INSERT TO bug6051 DO INSTEAD
  INSERT INTO bug6051_2
- SELECT NEW.i;
+ VALUES(NEW.i);
 WITH t1 AS ( DELETE FROM bug6051 RETURNING * )
 INSERT INTO bug6051 SELECT * FROM t1;
 SELECT * FROM bug6051;
@@ -1731,6 +1731,41 @@ SELECT * FROM bug6051_2;
  3
 (3 rows)
 
+-- check INSERT...SELECT rule actions are disallowed on commands
+-- that have modifyingCTEs
+CREATE OR REPLACE RULE bug6051_ins AS ON INSERT TO bug6051 DO INSTEAD
+ INSERT INTO bug6051_2
+ SELECT NEW.i;
+WITH t1 AS ( DELETE FROM bug6051 RETURNING * )
+INSERT INTO bug6051 SELECT * FROM t1;
+ERROR:  INSERT...SELECT rule actions are not supported for queries having data-modifying statements in WITH
+-- silly example to verify that hasModifyingCTE flag is propagated
+CREATE TEMP TABLE bug6051_3 AS
+  SELECT a FROM generate_series(11,13) AS a;
+CREATE RULE bug6051_3_ins AS ON INSERT TO bug6051_3 DO INSTEAD
+  SELECT i FROM bug6051_2;
+BEGIN; SET LOCAL force_parallel_mode = on;
+WITH t1 AS ( DELETE FROM bug6051_3 RETURNING * )
+  INSERT INTO bug6051_3 SELECT * FROM t1;
+ i 
+---
+ 1
+ 2
+ 3
+ 1
+ 2
+ 3
+ 1
+ 2
+ 3
+(9 rows)
+
+COMMIT;
+SELECT * FROM bug6051_3;
+ a 
+---
+(0 rows)
+
 -- a truly recursive CTE in the same list
 WITH RECURSIVE t(a) AS (
        SELECT 0

diff --git a/src/test/regress/sql/with.sql b/src/test/regress/sql/with.sql
index 4869de4067d138f0a24fc5f9657de2e41f3428b2..a773795aaef41a8705bfee8e5bdadb2a0d5743d1 100644 (file)
--- a/src/test/regress/sql/with.sql
+++ b/src/test/regress/sql/with.sql
@@ -809,7 +809,7 @@ CREATE TEMP TABLE bug6051_2 (i int);
 
 CREATE RULE bug6051_ins AS ON INSERT TO bug6051 DO INSTEAD
  INSERT INTO bug6051_2
- SELECT NEW.i;
+ VALUES(NEW.i);
 
 WITH t1 AS ( DELETE FROM bug6051 RETURNING * )
 INSERT INTO bug6051 SELECT * FROM t1;
@@ -817,6 +817,31 @@ INSERT INTO bug6051 SELECT * FROM t1;
 SELECT * FROM bug6051;
 SELECT * FROM bug6051_2;
 
+-- check INSERT...SELECT rule actions are disallowed on commands
+-- that have modifyingCTEs
+CREATE OR REPLACE RULE bug6051_ins AS ON INSERT TO bug6051 DO INSTEAD
+ INSERT INTO bug6051_2
+ SELECT NEW.i;
+
+WITH t1 AS ( DELETE FROM bug6051 RETURNING * )
+INSERT INTO bug6051 SELECT * FROM t1;
+
+-- silly example to verify that hasModifyingCTE flag is propagated
+CREATE TEMP TABLE bug6051_3 AS
+  SELECT a FROM generate_series(11,13) AS a;
+
+CREATE RULE bug6051_3_ins AS ON INSERT TO bug6051_3 DO INSTEAD
+  SELECT i FROM bug6051_2;
+
+BEGIN; SET LOCAL force_parallel_mode = on;
+
+WITH t1 AS ( DELETE FROM bug6051_3 RETURNING * )
+  INSERT INTO bug6051_3 SELECT * FROM t1;
+
+COMMIT;
+
+SELECT * FROM bug6051_3;
+
 -- a truly recursive CTE in the same list
 WITH RECURSIVE t(a) AS (
        SELECT 0