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Commit6f19a8c

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Teach eval_const_expressions to constant-fold LEAST/GREATEST expressions.
Doing this requires an assumption that the invoked btree comparisonfunction is immutable. We could check that explicitly, but in otherplaces such as contain_mutable_functions we just assume that it's true,so we may as well do likewise here. (If the comparison function'sbehavior isn't immutable, the sort order in indexes built with it wouldbe unstable, so it seems certainly wrong for it not to be so.)Vik FearingDiscussion:https://postgr.es/m/c6e8504c-4c43-35fa-6c8f-3c0b80a912cc@2ndquadrant.com
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‎src/backend/optimizer/util/clauses.c

Lines changed: 6 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -3378,11 +3378,16 @@ eval_const_expressions_mutator(Node *node,
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caseT_ArrayRef:
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caseT_ArrayExpr:
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caseT_RowExpr:
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caseT_MinMaxExpr:
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{
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/*
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* Generic handling for node types whose own processing is
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* known to be immutable, and for which we need no smarts
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* beyond "simplify if all inputs are constants".
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*
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* Treating MinMaxExpr this way amounts to assuming that the
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* btree comparison function it calls is immutable; see the
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* reasoning in contain_mutable_functions_walker.
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*/
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/* Copy the node and const-simplify its arguments */
@@ -3783,7 +3788,7 @@ eval_const_expressions_mutator(Node *node,
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caseT_ConvertRowtypeExpr:
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{
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ConvertRowtypeExpr*cre=castNode(ConvertRowtypeExpr,node);
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Node*arg;
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Node*arg;
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ConvertRowtypeExpr*newcre;
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arg=eval_const_expressions_mutator((Node*)cre->arg,

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