Thread: pgsql: Simplify overcomplicated (and overly restrictive) test to see
pgsql: Simplify overcomplicated (and overly restrictive) test to see
From
tgl@postgresql.org (Tom Lane)
Date:
Log Message: ----------- Simplify overcomplicated (and overly restrictive) test to see whether an IS NULL condition is rendered redundant by detection of an antijoin. If we know that a join is an antijoin, then *any* Var coming out of its righthand side must be NULL, not only the joining column(s). Also, it's still gonna be null after being passed up through higher joins, whether they're outer joins or not. I was misled by a faulty analogy to reduce_outer_joins() in the original coding. But consider select * from a left join b on a.x = b.y where b.y is null and b.z is null; The first IS NULL condition justifies deciding that the join is an antijoin (if the = is strict) and then the second one is just plain redundant. Modified Files: -------------- pgsql/src/backend/optimizer/plan: initsplan.c (r1.146 -> r1.147) (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/optimizer/plan/initsplan.c?r1=1.146&r2=1.147)