Le jeudi 19 juin 2014 16:10:19 UTC+3, Michael Bayer a écrit :
>
>
> On 6/19/14, 4:09 AM, Mike Solomon wrote:
> >
> >
> >
> > It's difficult to issue a straight SQL string for the hybrid property
> > itself because
>
>
> sorry, I meant, please write the query *that you really want* as a SQL
> string. Don't use SQLAlchemy. It's better to work in that direction.
>
> If you don't know what the SQL you want is, that's a different issue,
> I'd start on that part first.
>
Ah, OK. The SQL below will group fractions based on tag and give the
num(erator) and den(ominator) of the maximum for each group. In Python, I'd
like to have a fraction class that has members tag and val where val is a
hybrid_property combining num and den. I'd like to be able to do a query
like session.query(Fraction.tag,
func.max(Fraction.val)).group_by(Fraction.tag) and get the SQL below:
CREATE TABLE fraction (
id Int,
tag Int,
num Int,
den Int,
PRIMARY KEY (id)
);
SELECT DISTINCT fraction_a.tag, fraction_a.high,
fraction_b.num, fraction_b.den
FROM
(SELECT fraction.tag, max(1.0 * fraction.num / fraction.den) AS high
FROM fraction
GROUP BY fraction.tag)
AS fraction_a JOIN
(SELECT fraction.tag, fraction.num, fraction.den
FROM fraction)
AS fraction_b
ON fraction_a.tag = fraction_b.tag
AND fraction_a.high = 1.0 * fraction_b.num / fraction_b.den;
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