轉換嵌套查詢到加盟

Question

我的查詢是

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) 

的DISTINCT是必要的，以保持行被乘以在所有行其他表匹配。

Answer 2

試試這個：

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

Answer 3

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