pgsql: Clear more substructure of a dead relation during join removal.

Clear more substructure of a dead relation during join removal.

The tablesample and securityQuals subtrees of a RangeTblEntry can
include Vars, which will cause trouble if they point at a removed
rel and are visited during later processing. Hence, clear those
fields during join removal, as we already do for the subquery field.
remove_useless_outer_joins got this right for securityQuals but
not tablesample, while remove_self_join_rel missed doing it for
securityQuals. (It escapes trouble for tablesample only because we
made a policy decision to never touch sampled relations for SJE.)

Oversight in 2ebf25e7d. Back-patch to v16, like that commit
(but the SJE issue only goes as far back as v18).

Author: shihao zhong <zhong950419(at)gmail(dot)com>
Reviewed-by: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Discussion: https://postgr.es/m/CAGRkXqSOAT1yop44B8jwacL_91rxK=QuoU8Of3NLMb9NgAO2NA@mail.gmail.com
Backpatch-through: 16

Branch
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REL_17_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/12f10c25ce3febf9b94748d28c8332f827779980

Modified Files
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src/backend/optimizer/plan/analyzejoins.c | 8 +++++---
1 file changed, 5 insertions(+), 3 deletions(-)