简单的SQL问题(mysql)

Question

SELECT username, (SELECT follow 
                  FROM follow 
                  WHERE follow_user_id = user_id) AS following
FROM user
WHERE user_id = 1

我想知道如何检查是否follow(sub-query(select follow ...))返回一个值.如果是,请将其替换为"是".如果没有,则将其替换为"否".

Answer 1

使用案例陈述

select username, 
  Case When Exists 
      (select * from follow 
       where follow_user_id = user_id)
    Then 'Yes' Else 'No' End following
from user
where user_id = 1