Actually, i tried to make this query using NOT IN, i made something like
this:
SELECT courses.*
FROM courses
INNER JOIN courses_times ON courses_times.course_id = courses.id
INNER JOIN times ON courses_times.time_id = times.id
where courses.id
NOT IN (
SELECT courses.id
FROM courses
INNER JOIN courses_times ON courses_times.course_id = courses.id
INNER JOIN times ON courses_times.time_id = times.id
AND times.day != 'Monday'
)
AND times.day = 'Monday'
But, its not very useful, im using MySql, and it wasted like 30 seconds to
give me the result.. o.O
its because my tables have a lot of registers: coursers (8000), times
(300), courses_times (1300)
Does anyone have another ideia for this query?
Fernando
2011/1/5 Frederick Cheung <[email protected]>
>
>
> On Jan 5, 5:38 pm, Fernando Leandro <[email protected]>
> wrote:
>
> > When i use a query like above, for example, it returns to me all the
> courses
> > that have association with Monday,
> > it returns Math, Chimestry and History, and i would like to receive just
> > History
> >
> > I know that this question is not about rails but i need to solve this
> > problem to continue my rails app,
> > and i would appreciate if someone could help me..
> >
> > Does anyone have a solution for this?
>
> In sql terms, how about
>
> select *, count(*) as times_scheduled from course_times
> inner join course_times as other_times on other_times.course_id =
> course_times.course_id
> where course_times.time_id = 1
> group by course_times.course_id
> having times_scheduled = 1
>
> Arel is supposed to be way better than old skool activerecord at
> generating joins like this where you need to be careful about aliasing
> table names and so on.
>
> Fred
>
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