mysql - 将嵌套选择转换为连接

Question

我的查询是

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

试试这个:

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