Thomas Kellerer <spam_eater(at)gmx(dot)net> writes:
> So the optimizer _should_ be smart enough to do the conversion only
> once at the beginning of the statement and then use that converted
> value during the execution of the statement without the need
> to re-evaluate it for each row.
It's not; especially not in your originally posted case where the
up-conversion happens on the variable not the pseudo-constant.
regards, tom lane