mySQL may not allow subqueries... check the docs...

You could also try this syntax which is a little different...

SELECT a.UserID
FROM a
LEFT OUTER JOIN b on a.UserID = b.UserID
WHERE b.UserID is null


>hm.. but i only works in VFP, but returns syntax error when I put it in a mysql GUI program.. i though SQL syntax should be a standard.. any suggestion?
>
>thank a lot!!