Il giorno mercoledì 25 settembre 2013 08:46:15 UTC+2, onetwomany ha scritto: > > > > you can do that with >> >> all_courses = db(db.courses.id>0)._select(db.courses.memberid) >> all_members_not_in_courses = db(~db.members.id.belongs(all_courses)) >> >> >>> > Would such an approach be computationally expensive particularly if the > number of rows in courses is high? Perhaps the following raw SQL expression > would be more efficient: > > from gluon.dal import Expression > all_members_not_in_courses = db((db.members.id>0)&Expression(db, 'NOT > EXISTS (SELECT courses.memberid FROM courses WHERE courses.memberid= > members.id)')).select() >
oh boy, a MSSQL user, I guess :P .... The query plan is roughly equivalent. What instead would be beneficial is "inner selecting" a distinct set. -- Resources: - http://web2py.com - http://web2py.com/book (Documentation) - http://github.com/web2py/web2py (Source code) - https://code.google.com/p/web2py/issues/list (Report Issues) --- You received this message because you are subscribed to the Google Groups "web2py-users" group. To unsubscribe from this group and stop receiving emails from it, send an email to web2py+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/groups/opt_out.
