Counting one of multiple rows with same value for same ID

Question

Hello,
I have this query:
SELECT
count( case when EXISTS (
            SELECT *
            FROM  business_log bl, subject su
            WHERE  su.ID_SUBJECT = s.ID_SUBJECT
            and bl.id_subject = su.id_subject
            AND    bl.value = 'Solved'
then 1 else null end) num_solved
FROM subject s
It is posible that one subject is more than once 'Solved' in table BUSINESS_LOG
I want to count only one row solved for one subject.
I must to use only SUBJECT table in the main query because of other counts.
Thank You very much.
Regards
Milos
Message was edited by: 2796614

Answer 1

so in case you have no solved entry...you get NULL back instead of 0.....
and....there is no need for the group by ....as you are only looking for one subject
SELECT COALESCE((SELECT max(1)
                  FROM  business_log bl
                 WHERE bl.id_subject = s.id_subject
                   AND bl.value = 'Solved'),0) num_solved
  FROM subject s
but....I would like to have a proof, that this one is faster than the outer-join solution.
So...perhaps we'll see an execution plan for both of them.
corrected....missing bracket