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## pgsql: Allow predicate_refuted_by() to deduce that NOT A refutes A.

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Log Message: ----------- Allow predicate_refuted_by() to deduce that NOT A refutes A. We had originally made the stronger assumption that NOT A refutes any B if B implies A, but this fails in three-valued logic, because we need to prove B is false not just that it's not true. However the logic does go through if B is equal to A. Recognizing this limited case is enough to handle examples that arise when we have simplified "bool_var = true" or "bool_var = false" to just "bool_var" or "NOT bool_var". If we had not done that simplification then the btree-operator proof logic would have been able to prove that the expressions were contradictory, but only for identical expressions being compared to the constants; so handling identical A and B covers all the same cases. The motivation for doing this is to avoid unexpected asymmetrical behavior when a partitioned table uses a boolean partitioning column, as in today's gripe from Dominik Sander. Back-patch to 8.2, which is as far back as predicate_refuted_by attempts to do anything at all with NOTs. Tags: ---- REL8_2_STABLE Modified Files: -------------- pgsql/src/backend/optimizer/util: predtest.c (r1.10.2.5 -> r1.10.2.6) (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/optimizer/util/predtest.c?r1=1.10.2.5&r2=1.10.2.6)

Next: From:Bruce MomjianDate:2010-02-25 22:24:00Subject: pgsql: Document that after triggers that need to see changed rows shouldPrevious: From: Tom LaneDate: 2010-02-25 21:00:10Subject: pgsql: Allow predicate_refuted_by() to deduce that NOT A refutes A.