pgsql: Handle SubPlan cases in find_nonnullable_rels/vars.

Handle SubPlan cases in find_nonnullable_rels/vars.

We can use some variants of SubPlan to deduce that Vars appearing
in the testexpr must be non-null.

Richard Guo

Discussion: /messages/by-id/CAMbWs4-jV=199A2Y_6==99dYnpnmaO_Wz_RGkRTTaCB=Pihw2w@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/ff8fa0bf7eb9001f321c2af4bbe9c0f2bd5c1bf8

Modified Files
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src/backend/optimizer/util/clauses.c | 34 ++++++++++++++++++++++++++++++++++
src/test/regress/expected/join.out | 28 ++++++++++++++++++++++++++++
src/test/regress/sql/join.sql | 13 +++++++++++++
3 files changed, 75 insertions(+)