Question

I’m trying to retrieve all the users ids who have their preferences (IN (1,7) AND (2)). Even without the group on user_id. It doesn’t work. Any idea would be very helpful.

HasPreference.find(:all, :conditions  => ["preference_id IN (1,7) AND preference_id = 2"], :group  => :user_id)

TABLE is ‘has_preferences’

ID -- PREFERENCE_ID -- USER_ID

1  --       2       --    1

1  --       7       --    1

1  --       1       --    1

1  --       2       --    2

I’d like to get [1] as a result.

Thanks

Answer 1

SELECT  user_id
FROM    has_preferences
WHERE   preference_id = 2
        AND user_id IN
        (
        SELECT  user_id
        FROM    has_preferences
        WHERE   preference_id IN (1, 7)
        )

Create an index on (preference_id, user_id) for this to work fast.