组合或交叉多个 MySQL 命令

Question

我必须搜索两个 table。

我的第二个table是：

+---------+---------------+-------+
| user_id | is_first_time | score |
+---------+---------------+-------+
|   44    |       1       |   20  |
+---------+---------------+-------+
|   44    |       0       |   20  |
+---------+---------------+-------+

我的第一个table只包含用户信息。

如果我使用下面的MySQL命令，我会得到一个结果：

SELECT * , users_score.user_id users_score_user_id 
FROM users JOIN users_score 
ON users_score.user_id = users.id 
WHERE (users_score.score='20' AND users_score.is_first_time='1')

如果我使用下面的MySQL命令，我也会得到一个结果（我只是将"is_first_time"值改为“0”：

SELECT * , users_score.user_id users_score_user_id 
FROM users JOIN users_score 
ON users_score.user_id = users.id 
WHERE (users_score.score='20' AND users_score.is_first_time='0')

但是如果我用 AND 组合这两个命令，我将不会得到任何结果：

SELECT * , users_score.user_id users_score_user_id 
FROM users JOIN users_score 
ON users_score.user_id = users.id 
WHERE (users_score.score='20' AND users_score.is_first_time='1')
AND (users_score.score='20' AND users_score.is_first_time='0')

如何合并或交叉这两个命令？

感谢您的帮助。

Answer 1

这里需要使用OR条件

WHERE (users_score.score='20' AND users_score.is_first_time='1') 
  OR  (users_score.score='20' AND users_score.is_first_time='0')

但是可以用IN条件

写得更好

SELECT *,
       users_score.user_id users_score_user_id
FROM   users
       JOIN users_score
         ON users_score.user_id = users.id
WHERE  users_score.score = '20'
       AND users_score.is_first_time IN ( '1', '0' )

Answer 2

如果您希望用户同时满足两个条件，则一种方法使用 in 或 exists:

SELECT u.* 
FROM users u
WHERE u.id IN (SELECT us.user_id FROM users_score us WHERE us.score = '20' AND us.is_first_time = '0'
              ) AND
      u.id IN (SELECT us.user_id FROM users_score us WHERE us.score = '20' AND us.is_first_time = '1'
              );

AND 的问题是单行不能同时为 0 和 1。

如果你只想要用户 ID，我会推荐 group by 和 having:

select us.user_id
from users_score us
where score = 20 and us.is_first_time in (0, 1)
group by us.user_id
having count(distinct us.is_first_time) = 2;

请注意，我删除了单引号。如果列是数字，则不要使用单引号进行比较。（当然，如果是字符串，就用单引号）

组合或交叉多个 MySQL 命令

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