Joel
Check out using WL functions in the 'Calculated Item' section of the Query generator.
I have not tried this sort of thing from there myself!
Failing that then edit the sql code direct (you will lose the graphical query display).
I added the last line of the Select statement and the WHERE clause (in Blue).
Something like the code below should do the trick.
I have not tested this but I do have similar code working.
SELECT
MemberMain.idMemberMain AS idMemberMain,
MemberMain.MembershipNo AS MembershipNo,
MemberMain.DateJoined AS DateJoined,
WL.DateSys() AS Today
FROM
MemberMain
WHERE
MemberMain.DateJoined <= Today
HTH
Regards
DerekT