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Commit37b4e0f

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Make setrefs.c match by ressortgroupref even for plain Vars.
Previously, we skipped using search_indexed_tlist_for_sortgroupref()if the tlist expression being sought in the child plan node was merelya Var. This is purely an optimization, based on the theory thatsearch_indexed_tlist_for_var() is faster, and one copy of a Var shouldbe as good as another. However, the GROUPING SETS patch broke thelatter assumption: grouping columns containing the "same" Var cansometimes have different outputs, as shown in the test case added here.So do it the hard way whenever a ressortgroupref marking exists.(If this seems like a bottleneck, we could imagine building a tlist indexdata structure for ressortgroupref values, as we do for Vars. But I'lllet that idea go until there's some evidence it's worthwhile.)Back-patch to 9.6. The problem also exists in 9.5 where GROUPING SETScame in, but this patch is insufficient to resolve the problem in 9.5:there is some obscure dependency on the upper-planner-pathificationwork that happened in 9.6. Given that this is such a weird corner case,and no end users have complained about it, it doesn't seem worth the workto develop a fix for 9.5.Patch by me, per a report from Heikki Linnakangas. (This does not fixHeikki's original complaint, just the follow-on one.)Discussion:https://postgr.es/m/aefc657e-edb2-64d5-6df1-a0828f6e9104@iki.fi
1 parentea8480a commit37b4e0f

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3 files changed

+42
-3
lines changed

3 files changed

+42
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lines changed

‎src/backend/optimizer/plan/setrefs.c

Lines changed: 2 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -1687,8 +1687,8 @@ set_upper_references(PlannerInfo *root, Plan *plan, int rtoffset)
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TargetEntry*tle= (TargetEntry*)lfirst(l);
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Node*newexpr;
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1690-
/* If it's anon-Varsort/group item, first try to match by sortref */
1691-
if (tle->ressortgroupref!=0&& !IsA(tle->expr,Var))
1690+
/* If it's a sort/group item, first try to match by sortref */
1691+
if (tle->ressortgroupref!=0)
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{
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newexpr= (Node*)
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search_indexed_tlist_for_sortgroupref((Node*)tle->expr,
@@ -2049,7 +2049,6 @@ search_indexed_tlist_for_non_var(Node *node,
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20502050
/*
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* search_indexed_tlist_for_sortgroupref --- find a sort/group expression
2052-
*(which is assumed not to be just a Var)
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*
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* If a match is found, return a Var constructed to reference the tlist item.
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* If no match, return NULL.

‎src/test/regress/expected/groupingsets.out

Lines changed: 29 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -352,6 +352,35 @@ select a, d, grouping(a,b,c)
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2 | 2 | 2
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(4 rows)
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-- check that distinct grouping columns are kept separate
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-- even if they are equal()
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explain (costs off)
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select g as alias1, g as alias2
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from generate_series(1,3) g
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group by alias1, rollup(alias2);
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QUERY PLAN
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------------------------------------------------
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GroupAggregate
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Group Key: g, g
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Group Key: g
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-> Sort
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Sort Key: g
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-> Function Scan on generate_series g
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(6 rows)
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select g as alias1, g as alias2
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from generate_series(1,3) g
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group by alias1, rollup(alias2);
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alias1 | alias2
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--------+--------
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1 | 1
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1 |
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2 | 2
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2 |
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3 | 3
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3 |
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(6 rows)
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355384
-- simple rescan tests
356385
select a, b, sum(v.x)
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from (values (1),(2)) v(x), gstest_data(v.x)

‎src/test/regress/sql/groupingsets.sql

Lines changed: 11 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -130,6 +130,17 @@ select a, d, grouping(a,b,c)
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from gstest3
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group by grouping sets ((a,b), (a,c));
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-- check that distinct grouping columns are kept separate
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-- even if they are equal()
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explain (costs off)
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select gas alias1, gas alias2
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from generate_series(1,3) g
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group by alias1, rollup(alias2);
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select gas alias1, gas alias2
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from generate_series(1,3) g
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group by alias1, rollup(alias2);
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-- simple rescan tests
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select a, b,sum(v.x)

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