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Fix old oversight in const-simplification of COALESCE() expressions.

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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.
This commit is contained in:
Tom Lane 2010-11-12 15:14:51 -05:00
parent f5cf3ce7a4
commit faea083531
1 changed files with 5 additions and 1 deletions
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6
src/backend/optimizer/util/clauses.c
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@ -1774,7 +1774,9 @@ eval_const_expressions_mutator(Node *node,
/* /*
* We can remove null constants from the list. For a non-null * We can remove null constants from the list. For a non-null
* constant, if it has not been preceded by any other * 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)) if (IsA(e, Const))
{ {
@ -1782,6 +1784,8 @@ eval_const_expressions_mutator(Node *node,
continue; /* drop null constant */ continue; /* drop null constant */
if (newargs == NIL) if (newargs == NIL)
return e; /* first expr */ return e; /* first expr */
newargs = lappend(newargs, e);
break;
} }
newargs = lappend(newargs, e); newargs = lappend(newargs, e);
} }