it was suggested by someone last week, for ordering dates that can be null, to use something like order_by( "start_date is not null, start_date, end_date is null, end_date"), i.e. use extra prefixing/suffixing boolean expressions to subcategorize the actual values.
so depending on where do u want those rows with (B!=0, C==0 ->inf) and (B==0, C==0 --> nan), u can put some extra expressoins in the order_by. or use CASE On Wednesday 25 June 2008 21:05:34 Michael Bayer wrote: > On Jun 25, 12:36 pm, Dominique <[EMAIL PROTECTED]> wrote: > > Hello, > > > > A beginner question: > > I have a table with 4 columns: id, colA, colB, colC. > > I want to order (and make other operations as well ) the table > > asc or desc using the result of colB / colC knowing that colB and > > colC may equal to 0. > > > > When I try using query, the returned results are not correctly > > ordered: > > session.query(Mytable).order_by(asc(Mytable.colB / > > Mytable.colC)).all() > > I guess that the zero present in colB and colC may also interfere > > > > Is it possible to do this with queries with SA 0.4.6 ? > > Should I use select() and how or is it preferable to go for SA > > 0.5 ? > > it should be fine from a SQL generation perspective either way. To > confirm this turn on SQL echoing, most easily by passing > "echo=True" to your create_engine() call. As far as the ordering > actually working, I'm not sure about typical database behavior when > a division can result in a divide by zero - it would either raise > an error or produce a NaN value (I think the latter might be more > common). As far as how that orders you'd have to read the > documentation for the DB in use. To have explicit cases set up for > the divisor, use a CASE expression (which SQLA will generate for > you using the case() construct). > > > How should I do to get what I want ? > > > > Additional question: > > I ordered Essential SqlAlchemy on the French Amazon, but haven't > > received it yet (may be still on print ?). > > Does anybody know if it has been issued already in the US ? > > > > Many thanks in advance for helping me > > > > Dominique > > --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "sqlalchemy" group. To post to this group, send email to sqlalchemy@googlegroups.com To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en -~----------~----~----~----~------~----~------~--~---
