Jaime Casanova <systemguards(at)yahoo(dot)com> writes:
> What version of postgres are u using?
> I don't see that particular behavior in coalesce.
> someone knows if this is the behavior in any older
> version of pg?
Yes. Since about 7.4 COALESCE is a first-class expression node type,
but before that the parser expanded it into a CASE construct.
The CASE implementation is lacking in that it may evaluate the arguments
more than once, which could be wrong if they are volatile values.
regards, tom lane