On Apr 23, 2008, at 6:55 AM, Adrian wrote:
>
> I guess the solution to my problem is simple, although I did not
> manage to find it.
>
> The problem is as follows: I calculate the bray-curtis distance
> between an input and the rows in my table and give the value an alias
> ('brayCurtis'). What I want is to order the resultSet by brayCurtis
> and return only those rows where the value exceeds a given threshold.
> Ordering is pretty simple
>
> query = query.order_by(query.c.brayCurtis.desc())
>
> The problem occurs if I want to add an additional where clause like
> this:
>
> query = query.where(query.c.brayCurtis >= cutoff)
>
> Suddenly the whole statement is duplicated. Maybe there is a more
> concise and elegant solution for this problem.
Im not sure what "cutoff" is, but if its a SELECT statement, try using
cutoff.as_scalar(). This would solve the issue of extra elements
being added to the FROM clause, if thats whats happening.
But also, if cutoff is in fact a subquery, and the issue is that a
labeled column from the "columns" clause is not appearing as that
label in the WHERE clause, the subquery needs to be rendered at that
point. SQL doesnt officially allow order by or WHERE criterion based
on labels in the columns clause of the select statement - it will fail
on some databases, so SQLA currently doesn't place labels (i.e. column
AS foobar) anywhere outside the columns clause. A good optimizer
should figure out that the columns clause and WHERE clause are the
same thing.
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