Question

我正在尝试创建聊天应用，并希望启动用户1和2的对话。

表：

+----+---------------------+-----------+---------+
| id | message             | from_user | to_user |
+----+---------------------+-----------+---------+
|  1 | hello trick         |         1 |       2 |
|  2 | hi raf i am okay    |         2 |       1 |
|  3 | how is jo doing     |         1 |       2 |
|  4 | Hey                 |         2 |       3 |
|  5 | she is doing well   |         2 |       1 |
|  6 | how is kc doing     |         2 |       1 |
+----+---------------------+-----------+---------+

这是我的查询失败：

mysql> SELECT *
    -> FROM Messages
    -> WHERE from_user = 1
    -> AND to_user = 2
    -> AND to_user = 1
    -> AND from_user = 2;
Empty set (0.00 sec)

如何选择用户1和2的对话。我的设计对聊天应用程序有效吗？

预期产出：

+----+---------------------+-----------+---------+
| id | message             | from_user | to_user |
+----+---------------------+-----------+---------+
|  1 | hello trick         |         1 |       2 |
|  2 | hi raf i am okay    |         2 |       1 |
|  3 | how is jo doing     |         1 |       2 |
|  5 | she is doing well   |         2 |       1 |
|  6 | how is kc doing     |         2 |       1 |
+----+---------------------+-----------+---------+

ORDER BY id可能是必要的

Answer 1

这应该这样做。

SELECT *
    FROM Messages
    WHERE (from_user = 1 AND to_user = 2)
       OR (from_user = 2 AND to_user = 1);

Answer 2

单行不能同时拥有to_user=1和to_user=2，因此此查询不会返回任何行。相反，您需要使用逻辑or运算符来区分两个＆＃34;方向＆＃34;谈话：

SELECT *
FROM   messages
WHERE  (from_user = 1 AND to_user = 2) OR (to_user = 1 AND from_user = 2)

如何做多个封装的WHERE子句

3 个答案: