Question

My query is

select COUNT(*) from result 
where test_id in (select test_id 
                    from test_schedule 
                    where scheduler_id in (select user_id 
                                           from users 
                                           where user_type=1))

Answer 1

SELECT COUNT(*)
FROM result r
JOIN (SELECT DISTINCT test_id
      FROM test_schedule s
      JOIN users u ON s.scheduler_id = u.user_id
      WHERE u.user_type = 1) s
USING (test_id)

The DISTINCT is necessary to keep rows from being multiplied by all the rows in the other tables that match.