Fix oversight in flattening of subqueries with empty FROM.
I missed a restriction that commit f4abd0241de20d5d6a79b84992b9e88603d44134
should have enforced: we can't pull up an empty-FROM subquery if it's under
an outer join, because then we'd need to wrap its output columns in
PlaceHolderVars. As the code currently stands, the PHVs end up with empty
relid sets, which doesn't work (and is correctly caught by an Assert).
It's possible that this could be fixed by assigning the PHVs the relid
sets of the parent FromExpr/JoinExpr, but getting that to work is more
complication than I care to add right now; indeed it's likely that
we'll never bother, since pulling up empty-FROM subqueries is a rather
marginal optimization anyway.
Per report from Andreas Seltenreich. Back-patch to 9.5 where the faulty
code was added.
Branch
------
REL9_5_STABLE
Details
-------
http://git.postgresql.org/pg/commitdiff/8fb61e0b5430b8dada0eca18b99e3956f4eaf6cd
Modified Files
--------------
src/backend/optimizer/prep/prepjointree.c | 52 +++++++++++++++++++----------
src/test/regress/expected/join.out | 34 +++++++++++++++++++
src/test/regress/sql/join.sql | 13 ++++++++
3 files changed, 81 insertions(+), 18 deletions(-)