From: | tgl(at)postgresql(dot)org (Tom Lane) |
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To: | pgsql-committers(at)postgresql(dot)org |
Subject: | pgsql: Allow predicate_refuted_by() to deduce that NOT A refutes A. |
Date: | 2010-02-25 21:00:10 |
Message-ID: | 20100225210010.89DE57541D1@cvs.postgresql.org |
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Log Message:
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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We had originally made the stronger assumption that NOT A refutes any B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:
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REL8_3_STABLE
Modified Files:
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pgsql/src/backend/optimizer/util:
predtest.c (r1.19.2.2 -> r1.19.2.3)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/optimizer/util/predtest.c?r1=1.19.2.2&r2=1.19.2.3)
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