seems like a job for distinct=True (or a groupby) . Docs are here <http://web2py.com/books/default/chapter/29/06/the-database-abstraction-layer#orderby--groupby--limitby--distinct--having-orderby_on_limitby-left-cache>
On Wednesday, January 21, 2015 at 7:09:41 PM UTC+1, Spokes wrote: > > I'd like a db(query).select(...) operation to return a set of rows in > which there can only be one instance of a row with a particular value for a > certain field. My query is like this: > > book_query = ((db.t_article.f_book_id != None) & > (db.t_article.f_book_id == db.t_book_image.id)) > article_image_query = (db.t_article_image.f_article_id == > db.t_article.id) > query = [stuff pertaining to t_article] & (article_image_query | > book_query) > > The idea is to find all t_article entries within a certain time frame > (that's the stuff in brackets, which has been omitted), which either have > an image associated with them, or which reference a t_book entry which has > an image associated with it. > > The select statement is like this: > > rows = db(query).select(limitby = (0, number_of_records), orderby = > '<random>') > > I'd like the select statement to return no more than one row with a > particular value for the f_book_id field. With the above select() statement > as it is, it's possible for rows[0]['t_article']['f_book_id'], > rows[1]['t_article']['f_book_id'], and rows[2]['t_article']['f_book_id'], > for example, to have the same value. Is it possible to modify the above > code so that in situations like the preceding, only one of those rows > (doesn't matter which one) is returned, and assigned to the rows object? > Thanks. > -- 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 [email protected]. For more options, visit https://groups.google.com/d/optout.
