Fix edge case in remove_useless_result_rtes() with outer joins. find_dependent_phvs() and find_dependent_phvs_in_jointree() decide whether a PlaceHolderVar depends on the RTE_RESULT rel we're considering removing by comparing the PHV's phrels to a singleton set containing that rel's RT index, reasoning that if phrels contains any other relid bits then those define an appropriate place where we can evaluate the PHV. But since this code was originally written, we've redefined phrels to include outer-join relids, and that breaks this logic, potentially allowing us to remove an RTE_RESULT that leaves no valid place to evaluate the PHV. The planner doesn't throw an error when that happens, but it does produce an incorrect plan that will not replace the PHV's value with NULL when needed.
In the known test case for this bug, the "extra" OJ relid is one that we've actually decided to remove but haven't yet cleaned out of the query's PHVs. It's not entirely clear though that that would always be the case. Let's restore this code to the way it was designed to work, by considering only base relids within the PHV's phrels. Bug: #19553 Reported-by: Viktor Leis <[email protected]> Author: Matheus Alcantara <[email protected]> Co-authored-by: Richard Guo <[email protected]> Reviewed-by: Tom Lane <[email protected]> Discussion: https://postgr.es/m/[email protected] Backpatch-through: 16 Branch ------ REL_16_STABLE Details ------- https://git.postgresql.org/pg/commitdiff/3e1fe25e686d788a32c926e2aa79bc8d9312841b Modified Files -------------- src/backend/optimizer/prep/prepjointree.c | 64 ++++++++++++++++++++++++------- src/test/regress/expected/join.out | 27 +++++++++++++ src/test/regress/sql/join.sql | 10 +++++ 3 files changed, 88 insertions(+), 13 deletions(-)
