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跟随（子查询（选择跟随...））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

Answer 2

SELECT u.username，IF（（SELECT COUNT（*）FROM follow f WHERE f.follow_user_id = u.user_id），“yes”，“no”）FROM user u WHERE u.user_id = 1

简单的SQL问题（mysql）

2 个答案: