Question

我的数据库有两个表，一个表包含有关用户的信息，另一个表包含用户之间的事务列表。我想在第二个表中选择行，用用户名替换电子邮件。

ACCOUNTS
----------------------------------------------
     email      | password | username | token
----------------------------------------------
 joe@mail.com   | xxxxxxxx | joe      | abcde
----------------------------------------------
 bob@mail.com   | xxxxxxxx | bob      | edcba
----------------------------------------------

TRANSACTIONS
------------------------------------------------------
     sender     |   receiver   | amount   | timestamp
------------------------------------------------------
 joe@mail.com   | bob@mail.com | 20       | 123456789
------------------------------------------------------

EXPECTED RESULT
------------------------------------------------------
     sender     |   receiver   | amount   | timestamp
------------------------------------------------------
 joe            | bob          | 20       | 123456789
------------------------------------------------------

我试图做的是使用JOIN和UNION并使用以下查询：

SELECT amount, timestamp, accounts.username AS sender, accounts.username FROM tx JOIN accounts ON sender=accounts.email 
UNION 
SELECT amount, timestamp, accounts.username AS receiver, accounts.username FROM tx JOIN accounts ON receiver=accounts.email

当然不起作用，而是返回：

-----------------------------------------------------
     sender     |   receiver   | amount   | timestamp
-----------------------------------------------------
 joe            | joe          | 20       | 123456789
-----------------------------------------------------
 bob            | bob          | 20       | 123456789
-----------------------------------------------------

我的问题是，如何连接两个不同表的特定字段，并根据列的值在第二个表中选择行？谢谢！

P.S：我知道这个问题可能在互联网上某个地方有答案，但是我已经尝试了几种解决方案，但没有一个可行。

Answer 1

一种解决方案是两次JOIN accounts表，一次是发送方，一次是接收方：

SELECT
    c1.username sender,
    c2.username receiver,
    t.amount,
    t.timestamp
FROM transactions t
INNER JOIN accounts c1 ON c1.email = t.sender
INNER JOIN accounts c2 ON c2.email = t.receiver

MySQL-连接两个不同表的特定列

1 个答案: