pgsql: Don't assume a subquery's output is unique if there's a SRF in i

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

Branch
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REL9_3_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/6d36aee5b718524f718436d0973822bc2cb30bdd

Modified Files
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src/backend/optimizer/util/pathnode.c | 11 +++++++++++
src/test/regress/expected/subselect.out | 33 +++++++++++++++++++++++++++++++
src/test/regress/sql/subselect.sql | 9 +++++++++
3 files changed, 53 insertions(+)