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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

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`‎src/backend/optimizer/util/clauses.c`

Lines changed: 5 additions & 1 deletion

Original file line number	Diff line number	Diff line change
`@@ -2746,14 +2746,18 @@ eval_const_expressions_mutator(Node *node,`
`2746`	`2746`	`/*`
`2747`	`2747`	`* We can remove null constants from the list. For a non-null`
`2748`	`2748`	`* constant, if it has not been preceded by any other`
`2749`		`- * non-null-constant expressions then that is the result.`
	`2749`	`+ * non-null-constant expressions then it is the result. Otherwise,`
	`2750`	`+ * it's the next argument, but we can drop following arguments`
	`2751`	`+ * since they will never be reached.`
`2750`	`2752`	`*/`
`2751`	`2753`	`if (IsA(e,Const))`
`2752`	`2754`	`{`
`2753`	`2755`	`if (((Const*)e)->constisnull)`
`2754`	`2756`	`continue;/* drop null constant */`
`2755`	`2757`	`if (newargs==NIL)`
`2756`	`2758`	`returne;/* first expr */`
	`2759`	`+newargs=lappend(newargs,e);`
	`2760`	`+break;`
`2757`	`2761`	`}`
`2758`	`2762`	`newargs=lappend(newargs,e);`
`2759`	`2763`	`}`

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Commitd730424

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`‎src/backend/optimizer/util/clauses.c`

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