Fix EXPLAIN to handle SEARCH BREADTH FIRST queries

Enterprise / PostgreSQL - Tom Lane [sss.pgh.pa.us] - 16 September 2021 14:45 UTC

The rewriter transformation for SEARCH BREADTH FIRST produces a FieldSelect on a Var of type RECORD, where the Var references the recursive union's worktable output. EXPLAIN VERBOSE failed to handle this case, because it only expected such Vars to appear in CteScans not WorkTableScans. Fix that, and add some test cases exercising EXPLAIN on SEARCH and CYCLE queries.

In principle this oversight is an old bug, but it seems that the case is unreachable without SEARCH BREADTH FIRST, because the parser fails when attempting to create such a reference manually. So for today I'll just patch HEAD/v14. Someday we might find that the code portion of this patch needs to be back-patched further.

Per report from Atsushi Torikoshi.

Discussion: https://postgr.es/m/5bafa66ad529e11860339565c9e7c166@oss.nttdata.com

3f50b82639 Fix EXPLAIN to handle SEARCH BREADTH FIRST queries.
src/backend/utils/adt/ruleutils.c | 40 ++++++++++++--
src/test/regress/expected/with.out | 103 +++++++++++++++++++++++++++++++++++++
src/test/regress/sql/with.sql | 30 +++++++++++
3 files changed, 170 insertions(+), 3 deletions(-)

Upstream: git.postgresql.org


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