Got it now. In fact, I think this example is more meaningful than the one currently in the book to illustrate why one would want to nest select into belongs. Thanks.
On Wednesday, September 25, 2013 8:29:53 AM UTC+2, Niphlod wrote: > > it's explained pretty well on the book > > > http://web2py.com/books/default/chapter/29/06/the-database-abstraction-layer#belongs > > let me know if something is not clear > > Il giorno mercoledì 25 settembre 2013 07:11:27 UTC+2, step ha scritto: >> >> Niphlod, can you please explain why you're using method _select instead >> of select in your code below? In there no need to connect to SQL to set >> all_courses? >> >> On Tuesday, September 24, 2013 3:35:34 PM UTC+2, Niphlod wrote: >>> >>> 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)) >>> >>> you can eventually throw in a distinct on db.courses.memberid if the >>> number of courses rows is plenty. >>> >>> Il giorno martedì 24 settembre 2013 12:16:52 UTC+2, Michael Hall ha >>> scritto: >>>> >>>> I am not the most awesome SQL person and as such I am having trouble >>>> constructing a query I need. >>>> >>>> I have two tables in a database called "old". The parent table is >>>> called "members" and there is a child table called "courses". >>>> >>>> #-------- >>>> old.define_table('members', >>>> Field('id'), >>>> Field('profile_id','string'), >>>> Field('title','string'), >>>> Field('firstname','string'), >>>> Field('surname','string'), >>>> Field('memberlevel','string'), >>>> Field('lawfirm','string'), >>>> Field('registerdate','date'), >>>> Field('expirydate','date'), >>>> Field('email','string'), >>>> Field('telno','string'), >>>> Field('address1','string'), >>>> Field('address2','string'), >>>> Field('address3','string'), >>>> Field('town','string'), >>>> Field('county','string'), >>>> Field('postcode','string'), >>>> Field('country','string'), >>>> Field('notes','text'), >>>> Field('memberstatus','string'), >>>> migrate=False) >>>> >>>> old.define_table('courses', >>>> Field('memberid',type='reference members',), >>>> Field('profile_id','string'), >>>> Field('course','string'), >>>> Field('enroldate','string'), >>>> migrate=False) >>>> >>>> I would like to select all records in the members table that are not >>>> referenced by records in the courses table. I suppose it could be >>>> described >>>> as the opposite of a join as I only want to select members that do not >>>> have >>>> courses attached to them. >>>> >>>> Any help would be appreciated. >>>> >>>> >>>> -- 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.
