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Commitff8f710

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Prefer actual constants to pseudo-constants in equivalence class machinery.
generate_base_implied_equalities_const() should prefer plain Consts overother em_is_const eclass members when choosing the "pivot" value thatall the other members will be equated to. This makes it more likely thatthe generated equalities will be useful in constraint-exclusion proofs.Per report from Rushabh Lathia.
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‎src/backend/optimizer/path/equivclass.c‎

Lines changed: 8 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -768,15 +768,21 @@ generate_base_implied_equalities_const(PlannerInfo *root,
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}
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}
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771-
/* Find the constant member to use */
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/*
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* Find the constant member to use. We prefer an actual constant to
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* pseudo-constants (such as Params), because the constraint exclusion
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* machinery might be able to exclude relations on the basis of generated
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* "var = const" equalities, but "var = param" won't work for that.
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*/
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foreach(lc,ec->ec_members)
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{
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EquivalenceMember*cur_em= (EquivalenceMember*)lfirst(lc);
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if (cur_em->em_is_const)
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{
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const_em=cur_em;
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break;
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if (IsA(cur_em->em_expr,Const))
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break;
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}
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}
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Assert(const_em!=NULL);

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