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Commitfa21a76

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Don't assume a subquery's output is unique if there's a SRF in its tlist.
While the x output of "select x from t group by x" can be presumed unique,this does not hold for "select x, generate_series(1,10) from t group by x",because we may expand the set-returning function after the grouping step.(Perhaps that should be re-thought; but considering all the other odditiesinvolved with SRFs in targetlists, it seems unlikely we'll change it.)Put a check in query_is_distinct_for() so it's not fooled by such cases.Back-patch to all supported branches.David Rowley
1 parentd9d125d commitfa21a76

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3 files changed

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3 files changed

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‎src/backend/optimizer/util/pathnode.c

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@@ -1204,6 +1204,17 @@ query_is_distinct_for(Query *query, List *colnos, List *opids)
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Assert(list_length(colnos)==list_length(opids));
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/*
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* A set-returning function in the query's targetlist can result in
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* returning duplicate rows, if the SRF is evaluated after the
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* de-duplication step; so we play it safe and say "no" if there are any
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* SRFs. (We could be certain that it's okay if SRFs appear only in the
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* specified columns, since those must be evaluated before de-duplication;
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* but it doesn't presently seem worth the complication to check that.)
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*/
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if (expression_returns_set((Node*)query->targetList))
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return false;
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/*
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* DISTINCT (including DISTINCT ON) guarantees uniqueness if all the
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* columns in the DISTINCT clause appear in colnos and operator semantics

‎src/test/regress/expected/subselect.out

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@@ -742,3 +742,36 @@ select * from int4_tbl where
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0
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(1 row)
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--
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-- Check for incorrect optimization when IN subquery contains a SRF
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--
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set enable_hashjoin to 0;
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explain (verbose, costs off)
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select * from int4_tbl o where (f1, f1) in
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(select f1, generate_series(1,2) / 10 g from int4_tbl i group by f1);
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QUERY PLAN
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----------------------------------------------------------------
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Nested Loop Semi Join
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Output: o.f1
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Join Filter: (o.f1 = "ANY_subquery".f1)
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-> Seq Scan on public.int4_tbl o
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Output: o.f1
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-> Materialize
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Output: "ANY_subquery".f1, "ANY_subquery".g
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-> Subquery Scan on "ANY_subquery"
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Output: "ANY_subquery".f1, "ANY_subquery".g
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Filter: ("ANY_subquery".f1 = "ANY_subquery".g)
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-> HashAggregate
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Output: i.f1, (generate_series(1, 2) / 10)
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-> Seq Scan on public.int4_tbl i
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Output: i.f1
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(14 rows)
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select * from int4_tbl o where (f1, f1) in
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(select f1, generate_series(1,2) / 10 g from int4_tbl i group by f1);
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f1
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----
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0
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(1 row)
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reset enable_hashjoin;

‎src/test/regress/sql/subselect.sql

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Original file line numberDiff line numberDiff line change
@@ -422,3 +422,14 @@ select * from int4_tbl where
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select*from int4_tblwhere
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(case when f1in (select unique1from tenk1 a) then f1 elsenull end)in
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(select tenfrom tenk1 b);
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--
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-- Check for incorrect optimization when IN subquery contains a SRF
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--
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set enable_hashjoin to0;
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explain (verbose, costs off)
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select*from int4_tbl owhere (f1, f1)in
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(select f1, generate_series(1,2)/10 gfrom int4_tbl igroup by f1);
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select*from int4_tbl owhere (f1, f1)in
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(select f1, generate_series(1,2)/10 gfrom int4_tbl igroup by f1);
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reset enable_hashjoin;

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