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
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