Hello Stefan,
thanks for the feedback. I think I probably misstated my problem. I just
emailed a more explicit example of the sort of thing I am trying to do.
for the sake of completeness I'll reproduce it here:
table
id customer purchase
1 c1 microwave
2 c1 car
3 c1 freezer
4 c2 car
5 c2 microwave
6 c3 car
7 c3 CD player
the goal is to find all customers that have never bought a freezer.
am I correct in interpreting your suggestion, applied to this case, as
the query:
select customer from purchases where purchase != "freezer" is null
i tried and it returned zero rows. probably because purchase != freezer
is either true or false and neither value is null!
what am i missing?
Murad
"Stefan Hinz, iConnect (Berlin)" wrote:
>
> Dear Murad,
>
> > I know you can emulate an 'exists' subquery with a join. but I just
> > can't think of a way to emulate a 'not exists' without a subquery.
> > probably due to my limited sql experience. any hints?
>
> You have probably tried something like SELECT ... WHERE <condition> IS NOT
> NULL. To emulate a "not exists" subselect, you would use SELECT ... WHERE
> <condition> IS NULL.
>
> > BTW: when do you think mysql 4.1 would be stable enough for robust use
>
> As I hear, MySQL 4.1-alpha will be released very soon, probably in January.
> My guess for MySQL 4.1-gamma (the release declared as stable, meaning there
> are lots of installations in production environments that have proven
> stable) is August 2003. Any other guesses? Monty? ;-)
>
