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Commitfc1286d

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Fix rewriter to cope (more or less) with CTEs in the query being rewritten.
Since the original implementation of CTEs only allowed them in SELECTqueries, the rule rewriter did not expect to find any CTEs in statementsbeing rewritten by ON INSERT/UPDATE/DELETE rules. We had dealt with thisto some extent but the code was still several bricks shy of a load, asillustrated in bug #6051 from Jehan-Guillaume de Rorthais.In particular, we have to be able to copy CTEs from the original query'scteList into that of a rule action, in case the rule action references theCTE (which it pretty much always will). This also implies we were doingthings in the wrong order in RewriteQuery: we have to recursively rewritethe CTE queries before expanding the main query, so that we have therewritten queries available to copy.There are unpleasant limitations yet to resolve here, but at least we nowthrow understandable FEATURE_NOT_SUPPORTED errors for them instead of justfailing with bizarre implementation-dependent errors. In particular, wecan't handle propagating the same CTE into multiple post-rewrite queries(because then the CTE would be evaluated multiple times), and we can't copewith conflicts between CTE names in the original query and in the ruleactions.
1 parentdccfb72 commitfc1286d

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3 files changed

+189
-61
lines changed

3 files changed

+189
-61
lines changed

‎src/backend/rewrite/rewriteHandler.c

Lines changed: 126 additions & 61 deletions
Original file line numberDiff line numberDiff line change
@@ -454,6 +454,44 @@ rewriteRuleAction(Query *parsetree,
454454
}
455455
}
456456

457+
/*
458+
* If the original query has any CTEs, copy them into the rule action.
459+
* But we don't need them for a utility action.
460+
*/
461+
if (parsetree->cteList!=NIL&&sub_action->commandType!=CMD_UTILITY)
462+
{
463+
ListCell*lc;
464+
465+
/*
466+
* Annoying implementation restriction: because CTEs are identified
467+
* by name within a cteList, we can't merge a CTE from the original
468+
* query if it has the same name as any CTE in the rule action.
469+
*
470+
* This could possibly be fixed by using some sort of internally
471+
* generated ID, instead of names, to link CTE RTEs to their CTEs.
472+
*/
473+
foreach(lc,parsetree->cteList)
474+
{
475+
CommonTableExpr*cte= (CommonTableExpr*)lfirst(lc);
476+
ListCell*lc2;
477+
478+
foreach(lc2,sub_action->cteList)
479+
{
480+
CommonTableExpr*cte2= (CommonTableExpr*)lfirst(lc2);
481+
482+
if (strcmp(cte->ctename,cte2->ctename)==0)
483+
ereport(ERROR,
484+
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
485+
errmsg("WITH query name \"%s\" appears in both a rule action and the query being rewritten",
486+
cte->ctename)));
487+
}
488+
}
489+
490+
/* OK, it's safe to combine the CTE lists */
491+
sub_action->cteList=list_concat(sub_action->cteList,
492+
copyObject(parsetree->cteList));
493+
}
494+
457495
/*
458496
* Event Qualification forces copying of parsetree and splitting into two
459497
* queries one w/rule_qual, one w/NOT rule_qual. Also add user query qual
@@ -1805,6 +1843,69 @@ RewriteQuery(Query *parsetree, List *rewrite_events)
18051843
List*rewritten=NIL;
18061844
ListCell*lc1;
18071845

1846+
/*
1847+
* First, recursively process any insert/update/delete statements in WITH
1848+
* clauses. (We have to do this first because the WITH clauses may get
1849+
* copied into rule actions below.)
1850+
*/
1851+
foreach(lc1,parsetree->cteList)
1852+
{
1853+
CommonTableExpr*cte= (CommonTableExpr*)lfirst(lc1);
1854+
Query*ctequery= (Query*)cte->ctequery;
1855+
List*newstuff;
1856+
1857+
Assert(IsA(ctequery,Query));
1858+
1859+
if (ctequery->commandType==CMD_SELECT)
1860+
continue;
1861+
1862+
newstuff=RewriteQuery(ctequery,rewrite_events);
1863+
1864+
/*
1865+
* Currently we can only handle unconditional, single-statement DO
1866+
* INSTEAD rules correctly; we have to get exactly one Query out of
1867+
* the rewrite operation to stuff back into the CTE node.
1868+
*/
1869+
if (list_length(newstuff)==1)
1870+
{
1871+
/* Push the single Query back into the CTE node */
1872+
ctequery= (Query*)linitial(newstuff);
1873+
Assert(IsA(ctequery,Query));
1874+
/* WITH queries should never be canSetTag */
1875+
Assert(!ctequery->canSetTag);
1876+
cte->ctequery= (Node*)ctequery;
1877+
}
1878+
elseif (newstuff==NIL)
1879+
{
1880+
ereport(ERROR,
1881+
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
1882+
errmsg("DO INSTEAD NOTHING rules are not supported for data-modifying statements in WITH")));
1883+
}
1884+
else
1885+
{
1886+
ListCell*lc2;
1887+
1888+
/* examine queries to determine which error message to issue */
1889+
foreach(lc2,newstuff)
1890+
{
1891+
Query*q= (Query*)lfirst(lc2);
1892+
1893+
if (q->querySource==QSRC_QUAL_INSTEAD_RULE)
1894+
ereport(ERROR,
1895+
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
1896+
errmsg("conditional DO INSTEAD rules are not supported for data-modifying statements in WITH")));
1897+
if (q->querySource==QSRC_NON_INSTEAD_RULE)
1898+
ereport(ERROR,
1899+
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
1900+
errmsg("DO ALSO rules are not supported for data-modifying statements in WITH")));
1901+
}
1902+
1903+
ereport(ERROR,
1904+
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
1905+
errmsg("multi-statement DO INSTEAD rules are not supported for data-modifying statements in WITH")));
1906+
}
1907+
}
1908+
18081909
/*
18091910
* If the statement is an insert, update, or delete, adjust its targetlist
18101911
* as needed, and then fire INSERT/UPDATE/DELETE rules on it.
@@ -1983,67 +2084,6 @@ RewriteQuery(Query *parsetree, List *rewrite_events)
19832084
heap_close(rt_entry_relation,NoLock);
19842085
}
19852086

1986-
/*
1987-
* Recursively process any insert/update/delete statements in WITH clauses
1988-
*/
1989-
foreach(lc1,parsetree->cteList)
1990-
{
1991-
CommonTableExpr*cte= (CommonTableExpr*)lfirst(lc1);
1992-
Query*ctequery= (Query*)cte->ctequery;
1993-
List*newstuff;
1994-
1995-
Assert(IsA(ctequery,Query));
1996-
1997-
if (ctequery->commandType==CMD_SELECT)
1998-
continue;
1999-
2000-
newstuff=RewriteQuery(ctequery,rewrite_events);
2001-
2002-
/*
2003-
* Currently we can only handle unconditional, single-statement DO
2004-
* INSTEAD rules correctly; we have to get exactly one Query out of
2005-
* the rewrite operation to stuff back into the CTE node.
2006-
*/
2007-
if (list_length(newstuff)==1)
2008-
{
2009-
/* Push the single Query back into the CTE node */
2010-
ctequery= (Query*)linitial(newstuff);
2011-
Assert(IsA(ctequery,Query));
2012-
/* WITH queries should never be canSetTag */
2013-
Assert(!ctequery->canSetTag);
2014-
cte->ctequery= (Node*)ctequery;
2015-
}
2016-
elseif (newstuff==NIL)
2017-
{
2018-
ereport(ERROR,
2019-
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
2020-
errmsg("DO INSTEAD NOTHING rules are not supported for data-modifying statements in WITH")));
2021-
}
2022-
else
2023-
{
2024-
ListCell*lc2;
2025-
2026-
/* examine queries to determine which error message to issue */
2027-
foreach(lc2,newstuff)
2028-
{
2029-
Query*q= (Query*)lfirst(lc2);
2030-
2031-
if (q->querySource==QSRC_QUAL_INSTEAD_RULE)
2032-
ereport(ERROR,
2033-
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
2034-
errmsg("conditional DO INSTEAD rules are not supported for data-modifying statements in WITH")));
2035-
if (q->querySource==QSRC_NON_INSTEAD_RULE)
2036-
ereport(ERROR,
2037-
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
2038-
errmsg("DO ALSO rules are not supported for data-modifying statements in WITH")));
2039-
}
2040-
2041-
ereport(ERROR,
2042-
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
2043-
errmsg("multi-statement DO INSTEAD rules are not supported for data-modifying statements in WITH")));
2044-
}
2045-
}
2046-
20472087
/*
20482088
* For INSERTs, the original query is done first; for UPDATE/DELETE, it is
20492089
* done last. This is needed because update and delete rule actions might
@@ -2074,6 +2114,31 @@ RewriteQuery(Query *parsetree, List *rewrite_events)
20742114
}
20752115
}
20762116

2117+
/*
2118+
* If the original query has a CTE list, and we generated more than one
2119+
* non-utility result query, we have to fail because we'll have copied
2120+
* the CTE list into each result query. That would break the expectation
2121+
* of single evaluation of CTEs. This could possibly be fixed by
2122+
* restructuring so that a CTE list can be shared across multiple Query
2123+
* and PlannableStatement nodes.
2124+
*/
2125+
if (parsetree->cteList!=NIL)
2126+
{
2127+
intqcount=0;
2128+
2129+
foreach(lc1,rewritten)
2130+
{
2131+
Query*q= (Query*)lfirst(lc1);
2132+
2133+
if (q->commandType!=CMD_UTILITY)
2134+
qcount++;
2135+
}
2136+
if (qcount>1)
2137+
ereport(ERROR,
2138+
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
2139+
errmsg("WITH cannot be used in a query that is rewritten by rules into multiple queries")));
2140+
}
2141+
20772142
returnrewritten;
20782143
}
20792144

‎src/test/regress/expected/with.out

Lines changed: 40 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -1397,6 +1397,46 @@ SELECT * FROM y;
13971397
(17 rows)
13981398

13991399
DROP RULE y_rule ON y;
1400+
-- check merging of outer CTE with CTE in a rule action
1401+
CREATE TEMP TABLE bug6051 AS
1402+
select i from generate_series(1,3) as t(i);
1403+
SELECT * FROM bug6051;
1404+
i
1405+
---
1406+
1
1407+
2
1408+
3
1409+
(3 rows)
1410+
1411+
WITH t1 AS ( DELETE FROM bug6051 RETURNING * )
1412+
INSERT INTO bug6051 SELECT * FROM t1;
1413+
SELECT * FROM bug6051;
1414+
i
1415+
---
1416+
1
1417+
2
1418+
3
1419+
(3 rows)
1420+
1421+
CREATE TEMP TABLE bug6051_2 (i int);
1422+
CREATE RULE bug6051_ins AS ON INSERT TO bug6051 DO INSTEAD
1423+
INSERT INTO bug6051_2
1424+
SELECT NEW.i;
1425+
WITH t1 AS ( DELETE FROM bug6051 RETURNING * )
1426+
INSERT INTO bug6051 SELECT * FROM t1;
1427+
SELECT * FROM bug6051;
1428+
i
1429+
---
1430+
(0 rows)
1431+
1432+
SELECT * FROM bug6051_2;
1433+
i
1434+
---
1435+
1
1436+
2
1437+
3
1438+
(3 rows)
1439+
14001440
-- a truly recursive CTE in the same list
14011441
WITH RECURSIVE t(a) AS (
14021442
SELECT 0

‎src/test/regress/sql/with.sql

Lines changed: 23 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -610,6 +610,29 @@ SELECT * FROM y;
610610

611611
DROPRULE y_ruleON y;
612612

613+
-- check merging of outer CTE with CTE in a rule action
614+
CREATE TEMP TABLE bug6051AS
615+
select ifrom generate_series(1,3)as t(i);
616+
617+
SELECT*FROM bug6051;
618+
619+
WITH t1AS (DELETEFROM bug6051 RETURNING* )
620+
INSERT INTO bug6051SELECT*FROM t1;
621+
622+
SELECT*FROM bug6051;
623+
624+
CREATE TEMP TABLE bug6051_2 (iint);
625+
626+
CREATERULEbug6051_insASON INSERT TO bug6051 DO INSTEAD
627+
INSERT INTO bug6051_2
628+
SELECTNEW.i;
629+
630+
WITH t1AS (DELETEFROM bug6051 RETURNING* )
631+
INSERT INTO bug6051SELECT*FROM t1;
632+
633+
SELECT*FROM bug6051;
634+
SELECT*FROM bug6051_2;
635+
613636
-- a truly recursive CTE in the same list
614637
WITH RECURSIVE t(a)AS (
615638
SELECT0

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