MadHatter wrote:
> If I have an expression (a or b)a where a=TRUE and b=FALSE, why is b
> evaluated? Any true operand before an or operator means the entire
> expression is true .
There is no "before" - PG makes no guarantee about evaluation order.
Don't forget a,b might well be subqueries and you don't want to prevent
PG from applying optimisations.
> ---------------------------- EXAMPLE
>
> create or replace function pinsusers() returns trigger as
>
> $$
>
> declare msg varchar;
>
> begin
>
> --THROWS EXCEPTION when ((TG_OP = 'INSERT') is TRUE "record old
> is not assigned yet"
>
> msg = ((TG_OP = 'INSERT') or (new.password<>old.password));
You're looking at nested IF .. THEN's I'm afraid. Or using pl/perl or
similar.
--
Richard Huxton
Archonet Ltd