Fix PlaceHolderVar placement for join alias expressions When a join alias Var with nonempty varnullingrels expands to an expression that cannot carry the nullingrels itself, such as the RowExpr of a whole-row Var, add_nullingrels_if_needed() wraps it in a PlaceHolderVar. The choice of the PHV's phrels had several problems.
First, phrels was taken from all Vars in the expression. If a LATERAL subquery within the join has been pulled up, the expression can contain lateral references to rels outside the join, so the PHV could be evaluated above the outer join that is supposed to null it. This gave wrong results, or "wrong phnullingrels" errors. Second, for a variable-free expression we fell back to the join's relids but removed the join's own outer-join relid. That leaves a set spanning both sides of the outer join without the join itself, which can make the PHV look nullable by that join and cause "wrong phnullingrels" errors. Third, that fallback raised "unsupported join alias expression" when the Var is an outer reference from a subquery. The restriction is unnecessary: every planner caller passes root->parse as the query, so the Var always belongs to root->parse regardless of its varlevelsup. To fix, restrict phrels to the rels within the join, and if nothing is left, evaluate the PHV at the join including its outer-join relid, at any varlevelsup. Add an assertion that the query is root->parse. Author: Richard Guo <[email protected]> Discussion: https://postgr.es/m/CAMbWs49q_gvoeOoF0+KZ-DpQaDb=ngffsgrz2v_n1_64l4z...@mail.gmail.com Backpatch-through: 16 Branch ------ REL_16_STABLE Details ------- https://git.postgresql.org/pg/commitdiff/b03eb54b14010367b29305c32c8b80d01be4bcae Modified Files -------------- src/backend/optimizer/util/var.c | 26 ++-- src/test/regress/expected/join.out | 255 +++++++++++++++++++++++++++++++++++++ src/test/regress/sql/join.sql | 80 ++++++++++++ 3 files changed, 350 insertions(+), 11 deletions(-)
