From: Tom Lane Date: Fri, 7 Apr 2017 16:18:38 +0000 (-0400) Subject: Fix planner error (or assert trap) with nested set operations. X-Git-Tag: REL_10_BETA1~343 X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=89deca582a345b9c423bed8ebcf24b6ee81a9953;p=postgresql Fix planner error (or assert trap) with nested set operations. As reported by Sean Johnston in bug #14614, since 9.6 the planner can fail due to trying to look up the referent of a Var with varno 0. This happens because we generate such Vars in generate_append_tlist, for lack of any better way to describe the output of a SetOp node. In typical situations nothing really cares about that, but given nested set-operation queries we will call estimate_num_groups on the output of the subquery, and that wants to know what a Var actually refers to. That logic used to look at subquery->targetList, but in commit 3fc6e2d7f I'd switched it to look at subroot->processed_tlist, ie the actual output of the subquery plan not the parser's idea of the result. It seemed like a good idea at the time :-(. As a band-aid fix, change it back. Really we ought to have an honest way of naming the outputs of SetOp steps, which suggests that it'd be a good idea for the parser to emit an RTE corresponding to each one. But that's a task for another day, and it certainly wouldn't yield a back-patchable fix. Report: https://postgr.es/m/20170407115808.25934.51866@wrigleys.postgresql.org --- diff --git a/src/backend/optimizer/prep/prepunion.c b/src/backend/optimizer/prep/prepunion.c index b5cb4de6a2..881d85e26c 100644 --- a/src/backend/optimizer/prep/prepunion.c +++ b/src/backend/optimizer/prep/prepunion.c @@ -337,6 +337,16 @@ recurse_set_operations(Node *setOp, PlannerInfo *root, * Estimate number of groups if caller wants it. If the subquery used * grouping or aggregation, its output is probably mostly unique * anyway; otherwise do statistical estimation. + * + * XXX you don't really want to know about this: we do the estimation + * using the subquery's original targetlist expressions, not the + * subroot->processed_tlist which might seem more appropriate. The + * reason is that if the subquery is itself a setop, it may return a + * processed_tlist containing "varno 0" Vars generated by + * generate_append_tlist, and those would confuse estimate_num_groups + * mightily. We ought to get rid of the "varno 0" hack, but that + * requires a redesign of the parsetree representation of setops, so + * that there can be an RTE corresponding to each setop's output. */ if (pNumGroups) { @@ -346,7 +356,7 @@ recurse_set_operations(Node *setOp, PlannerInfo *root, *pNumGroups = subpath->rows; else *pNumGroups = estimate_num_groups(subroot, - get_tlist_exprs(subroot->processed_tlist, false), + get_tlist_exprs(subquery->targetList, false), subpath->rows, NULL); } diff --git a/src/test/regress/expected/union.out b/src/test/regress/expected/union.out index 4d697bada7..5c4edd1c16 100644 --- a/src/test/regress/expected/union.out +++ b/src/test/regress/expected/union.out @@ -320,6 +320,31 @@ SELECT q1 FROM int8_tbl EXCEPT ALL SELECT DISTINCT q2 FROM int8_tbl ORDER BY 1; SELECT q1 FROM int8_tbl EXCEPT ALL SELECT q1 FROM int8_tbl FOR NO KEY UPDATE; ERROR: FOR NO KEY UPDATE is not allowed with UNION/INTERSECT/EXCEPT +-- nested cases +(SELECT 1,2,3 UNION SELECT 4,5,6) INTERSECT SELECT 4,5,6; + ?column? | ?column? | ?column? +----------+----------+---------- + 4 | 5 | 6 +(1 row) + +(SELECT 1,2,3 UNION SELECT 4,5,6 ORDER BY 1,2) INTERSECT SELECT 4,5,6; + ?column? | ?column? | ?column? +----------+----------+---------- + 4 | 5 | 6 +(1 row) + +(SELECT 1,2,3 UNION SELECT 4,5,6) EXCEPT SELECT 4,5,6; + ?column? | ?column? | ?column? +----------+----------+---------- + 1 | 2 | 3 +(1 row) + +(SELECT 1,2,3 UNION SELECT 4,5,6 ORDER BY 1,2) EXCEPT SELECT 4,5,6; + ?column? | ?column? | ?column? +----------+----------+---------- + 1 | 2 | 3 +(1 row) + -- -- Mixed types -- diff --git a/src/test/regress/sql/union.sql b/src/test/regress/sql/union.sql index 48e6850798..5e0eff2ca3 100644 --- a/src/test/regress/sql/union.sql +++ b/src/test/regress/sql/union.sql @@ -112,6 +112,12 @@ SELECT q1 FROM int8_tbl EXCEPT ALL SELECT DISTINCT q2 FROM int8_tbl ORDER BY 1; SELECT q1 FROM int8_tbl EXCEPT ALL SELECT q1 FROM int8_tbl FOR NO KEY UPDATE; +-- nested cases +(SELECT 1,2,3 UNION SELECT 4,5,6) INTERSECT SELECT 4,5,6; +(SELECT 1,2,3 UNION SELECT 4,5,6 ORDER BY 1,2) INTERSECT SELECT 4,5,6; +(SELECT 1,2,3 UNION SELECT 4,5,6) EXCEPT SELECT 4,5,6; +(SELECT 1,2,3 UNION SELECT 4,5,6 ORDER BY 1,2) EXCEPT SELECT 4,5,6; + -- -- Mixed types --