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| author | Tom Lane <tgl@sss.pgh.pa.us> | 2014-07-08 14:03:14 -0400 |
|---|---|---|
| committer | Tom Lane <tgl@sss.pgh.pa.us> | 2014-07-08 14:03:56 -0400 |
| commit | 9e2f2d7a0539460dc76dbf76dfae17024d5e031e (patch) | |
| tree | 26f93c1bcfdcabbd04d0247feb58012d3ee37d05 /src/backend | |
| parent | 53166fe248c1b4b211094e80e54e5ab330dbf957 (diff) | |
| download | postgresql-9e2f2d7a0539460dc76dbf76dfae17024d5e031e.tar.gz postgresql-9e2f2d7a0539460dc76dbf76dfae17024d5e031e.zip | |
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
Diffstat (limited to 'src/backend')
| -rw-r--r-- | src/backend/optimizer/util/pathnode.c | 11 |
1 files changed, 11 insertions, 0 deletions
diff --git a/src/backend/optimizer/util/pathnode.c b/src/backend/optimizer/util/pathnode.c index 4e05dcd2463..d129f8d65ea 100644 --- a/src/backend/optimizer/util/pathnode.c +++ b/src/backend/optimizer/util/pathnode.c @@ -1474,6 +1474,17 @@ 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 * match. |