Question

我不知道为什么此SQL不返回任何行：

SELECT team_rel.team_id
     , team_rel.login_id 
  FROM team_rel
 INNER JOIN team ON team_rel.login_id = team.login_id
 WHERE team.login_id = '39' 
   AND NOT EXISTS (
         SELECT 0 
           FROM team_rel
          INNER JOIN team ON team_rel.login_id = team.login_id 
                         AND team_rel.login_id = '39' 
                         AND team_rel.team_id  = team.id
       )

同时执行以下SQL（相同，但没有NOT EXISTS条件）：

SELECT team_rel.team_id
     , team_rel.login_id 
  FROM team_rel
 INNER JOIN team ON team_rel.login_id = team.login_id
 WHERE team.login_id = '39'

返回：

+---------+----------+
| team_id | login_id |
+---------+----------+
|      23 |       39 |
+---------+----------+
|      23 |       39 |
+---------+----------+
|      13 |       39 |
+---------+----------+
|      13 |       39 |
+---------+----------+
|      16 |       39 |
+---------+----------+
|      16 |       39 |
+---------+----------+
|      25 |       39 |
+---------+----------+
|      25 |       39 |
+---------+----------+

和NOT EXISTS子查询（与SQL相同的SQL，对team_id进行测试）返回：

SELECT team_rel.team_id
     , team_rel.login_id 
  FROM team_rel
 INNER JOIN team ON team_rel.login_id = team.login_id
                AND team_rel.login_id = '39'
                AND team_rel.team_id = team.id

返回：

+---------+----------+
| team_id | login_id |
+---------+----------+
|      23 |       39 |
+---------+----------+
|      25 |       39 |
+---------+----------+

我希望我的第一个选择返回：

+---------+----------+
| team_id | login_id |
+---------+----------+
|      13 |       39 |
+---------+----------+
|      16 |       39 |
+---------+----------+

但是它不返回任何行吗？！

Answer 1

SELECT DISTINCT team_rel.team_id, team_rel.login_id 
FROM team_rel
INNER JOIN team ON team_rel.login_id = team.login_id
WHERE team_rel.login_id = 39
  AND team_rel.team_id NOT IN 
          (SELECT team_id FROM team_rel 
           INNER JOIN team ON team.id = team_rel.team_id AND
                              team.login_id = team_rel.login_id)

为什么此SQL返回null？

1 个答案: