Sql join，2表，相同字段

Question

我有2个表。为了简化：

表1中，用户：

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用户id INT， 的userName为nvarchar（50）

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表2中，消息：

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的msgId INT， msgFrom int， msgTo int ...

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msg1和msg2都包含userId。现在我想获取所有消息，但不是msgFrom我想要用户名。我知道该在这里做什么：

select tabMessages.*, tabUsers.userName as Sender 
     from tabMessages 
inner join tabUsers on msgFrom=userId 
where msgId = @someParameter; 

一切工作正常和丹迪。获取用户名而不是msgTo也是一样。现在的问题是，我该如何在同一个电话中获得BOTH字段？我想让表格成为

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msgId，msgFrom，msgTo，Sender，Recipient。我试图：

select tabMessages.*, tabUsers.userName as Sender, 
      tabUsers.userName as Recipient 
     from tabMessages 
inner join tabUsers on msgFrom=userId and msgTo=userId 
    where msgId = @someParameter; 

但这并不起作用。我正在使用Ms sql2000。

Answer 1

用不同的别名加入用户表两次。首先加入from列，第二加入to列。

select m.*, u1.userName as Sender, u2.userName as Recipient 
from tabMessages as m 
    inner join tabUsers as u1 
    on u1.userId=m.msgFrom 
    inner join tabUsers as u2 
    on u2.userId=m.msgTo 
where m.msgId = @someParameter; 

Answer 2

您需要加入到tabUsers两次。一个让发件人，一个让收件人：

SELECT m.*, f.userName as Sender, t.userName as Recipient 
FRPOM tabMessages AS m 
    INNER JOIN tabUsers AS f on m.msgFrom = f.userId 
    INNER JOIN tabUsers AS t on m.msgTo = t.userId 
WHERE m.msgId = @someParameter; 

Answer 3

你尝试UNION？

http://www.w3schools.com/sql/sql_union.asp