Don't remove an RTE_RESULT needed by a nested PlaceHolderVar When remove_useless_result_rtes() removes an RTE_RESULT, any PlaceHolderVars that were to be evaluated there must be evaluated somewhere else. If the RTE_RESULT is the nullable side of an outer join, there is no other place that would preserve the PHVs' nulling behavior, so find_dependent_phvs() refuses the removal if any such PHV exists anywhere in the query. If the RTE_RESULT is a child of an inner join, its PHVs can instead be evaluated at the join of all its sibling rels, unless a sibling needs them before that join is formed. find_dependent_phvs_in_jointree() checks for that by looking for such PHVs in the join quals and LATERAL RTEs of the siblings.
That misses a PHV that is evaluated at some but not all of the sibling rels and contains one of the RTE_RESULT's PHVs. Such a PHV can appear anywhere in the query, such as in the targetlist. This can happen when pulled-up expressions are wrapped in PHVs because of outer joins or grouping sets. Once the RTE_RESULT is removed, the outer PHV needs a value that is only available at a join above its own evaluation level. The outer PHV's rel thus becomes laterally dependent on the other sibling rels. If one of those rels laterally references it in turn, we end up with a rel that is laterally dependent on itself, causing an assertion failure in create_lateral_join_info(). To fix, also search the whole query for PHVs that are evaluated at some but not all of the sibling rels, and refuse to remove the RTE_RESULT if any of them contains one of its PHVs. An outer PHV that is evaluated at all of the sibling rels is not a problem, since the moved PHV is available there, so we don't block removal in that common case. Back-patch to all supported branches. Author: Richard Guo <[email protected]> Reviewed-by: Ayush Tiwari <[email protected]> Discussion: https://postgr.es/m/cambws4_hlosw8_sepp_3emytlx8oc4zezevypyprszpomhd...@mail.gmail.com Backpatch-through: 14 Branch ------ REL_16_STABLE Details ------- https://git.postgresql.org/pg/commitdiff/d87257b2cddc9a0f80bbb80d3190686aa983d9cd Modified Files -------------- src/backend/optimizer/prep/prepjointree.c | 69 ++++++++++++++++++++++++- src/test/regress/expected/join.out | 83 +++++++++++++++++++++++++++++++ src/test/regress/sql/join.sql | 34 +++++++++++++ 3 files changed, 184 insertions(+), 2 deletions(-)
