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 oddities
involved 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

diff --git a/src/backend/optimizer/util/pathnode.c b/src/backend/optimizer/util/pathnode.c
index 78aee5df08e6247e88c67f7a70c4a935bad20b8b..140d0004b51a6b26ebfab47fb39cd532df220ae3 100644 (file)
--- a/src/backend/optimizer/util/pathnode.c
+++ b/src/backend/optimizer/util/pathnode.c
@@ -1508,6 +1508,17 @@ query_is_distinct_for(Query *query, List *colnos, List *opids)
 
        Assert(list_length(colnos) == list_length(opids));
 
+       /*
+        * A set-returning function in the query's targetlist can result in
+        * returning duplicate rows, if the SRF is evaluated after the
+        * de-duplication step; so we play it safe and say "no" if there are any
+        * SRFs.  (We could be certain that it's okay if SRFs appear only in the
+        * specified columns, since those must be evaluated before de-duplication;
+        * but it doesn't presently seem worth the complication to check that.)
+        */
+       if (expression_returns_set((Node *) query->targetList))
+               return false;
+
        /*
         * DISTINCT (including DISTINCT ON) guarantees uniqueness if all the
         * columns in the DISTINCT clause appear in colnos and operator semantics

diff --git a/src/test/regress/expected/subselect.out b/src/test/regress/expected/subselect.out
index cde168e3c801f3af8c7828fec4520ef9bcd2640c..543709ac3fcac6a6f0d74c655d50df42e4142924 100644 (file)
--- a/src/test/regress/expected/subselect.out
+++ b/src/test/regress/expected/subselect.out
@@ -742,3 +742,36 @@ select * from int4_tbl where
   0
 (1 row)
 
+--
+-- Check for incorrect optimization when IN subquery contains a SRF
+--
+explain (verbose, costs off)
+select * from int4_tbl o where (f1, f1) in
+  (select f1, generate_series(1,2) / 10 g from int4_tbl i group by f1);
+                              QUERY PLAN                              
+----------------------------------------------------------------------
+ Hash Join
+   Output: o.f1
+   Hash Cond: (o.f1 = "ANY_subquery".f1)
+   ->  Seq Scan on public.int4_tbl o
+         Output: o.f1
+   ->  Hash
+         Output: "ANY_subquery".f1, "ANY_subquery".g
+         ->  HashAggregate
+               Output: "ANY_subquery".f1, "ANY_subquery".g
+               ->  Subquery Scan on "ANY_subquery"
+                     Output: "ANY_subquery".f1, "ANY_subquery".g
+                     Filter: ("ANY_subquery".f1 = "ANY_subquery".g)
+                     ->  HashAggregate
+                           Output: i.f1, (generate_series(1, 2) / 10)
+                           ->  Seq Scan on public.int4_tbl i
+                                 Output: i.f1
+(16 rows)
+
+select * from int4_tbl o where (f1, f1) in
+  (select f1, generate_series(1,2) / 10 g from int4_tbl i group by f1);
+ f1 
+----
+  0
+(1 row)
+

diff --git a/src/test/regress/sql/subselect.sql b/src/test/regress/sql/subselect.sql
index 326fd70e4a06bea8db43f24b878e1a79377c02b4..1975902726f99e02c2c4d579cd9869e529c13ff2 100644 (file)
--- a/src/test/regress/sql/subselect.sql
+++ b/src/test/regress/sql/subselect.sql
@@ -422,3 +422,12 @@ select * from int4_tbl where
 select * from int4_tbl where
   (case when f1 in (select unique1 from tenk1 a) then f1 else null end) in
   (select ten from tenk1 b);
+
+--
+-- Check for incorrect optimization when IN subquery contains a SRF
+--
+explain (verbose, costs off)
+select * from int4_tbl o where (f1, f1) in
+  (select f1, generate_series(1,2) / 10 g from int4_tbl i group by f1);
+select * from int4_tbl o where (f1, f1) in
+  (select f1, generate_series(1,2) / 10 g from int4_tbl i group by f1);