From 7b3c4a5d43e9529984ddbad501014f44d15bb34c Mon Sep 17 00:00:00 2001 From: Tom Lane Date: Fri, 12 Nov 2010 15:14:51 -0500 Subject: [PATCH] Fix old oversight in const-simplification of COALESCE() expressions. Once we have found a non-null constant argument, there is no need to examine additional arguments of the COALESCE. The previous coding got it right only if the constant was in the first argument position; otherwise it tried to simplify following arguments too, leading to unexpected behavior like this: regression=# select coalesce(f1, 42, 1/0) from int4_tbl; ERROR: division by zero It's a minor corner case, but a bug is a bug, so back-patch all the way. --- src/backend/optimizer/util/clauses.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/src/backend/optimizer/util/clauses.c b/src/backend/optimizer/util/clauses.c index 7094ed0c87c..c9904b4976b 100644 --- a/src/backend/optimizer/util/clauses.c +++ b/src/backend/optimizer/util/clauses.c @@ -2372,7 +2372,9 @@ eval_const_expressions_mutator(Node *node, /* * We can remove null constants from the list. For a non-null * constant, if it has not been preceded by any other - * non-null-constant expressions then that is the result. + * non-null-constant expressions then it is the result. Otherwise, + * it's the next argument, but we can drop following arguments + * since they will never be reached. */ if (IsA(e, Const)) { @@ -2380,6 +2382,8 @@ eval_const_expressions_mutator(Node *node, continue; /* drop null constant */ if (newargs == NIL) return e; /* first expr */ + newargs = lappend(newargs, e); + break; } newargs = lappend(newargs, e); }