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Commitfaea083

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Fix old oversight in const-simplification of COALESCE() expressions.
Once we have found a non-null constant argument, there is no need toexamine additional arguments of the COALESCE. The previous coding got itright only if the constant was in the first argument position; otherwiseit tried to simplify following arguments too, leading to unexpectedbehavior like this:regression=# select coalesce(f1, 42, 1/0) from int4_tbl;ERROR: division by zeroIt's a minor corner case, but a bug is a bug, so back-patch all the way.
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‎src/backend/optimizer/util/clauses.c

Lines changed: 5 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -1774,14 +1774,18 @@ eval_const_expressions_mutator(Node *node,
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/*
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* We can remove null constants from the list. For a non-null
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* constant, if it has not been preceded by any other
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* non-null-constant expressions then that is the result.
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* non-null-constant expressions then it is the result. Otherwise,
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* it's the next argument, but we can drop following arguments
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* since they will never be reached.
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*/
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if (IsA(e,Const))
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{
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if (((Const*)e)->constisnull)
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continue;/* drop null constant */
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if (newargs==NIL)
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returne;/* first expr */
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newargs=lappend(newargs,e);
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break;
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}
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newargs=lappend(newargs,e);
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}

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