INNER JOIN用于同一外键的两列

Question

假设我们有两个表:

表TA

AID BID1 BID2
--  ---- ----
01  01   02
02  01   03
03  02   01

表TB

BID Name
--- ----
01  FOO
02  BOO
03  LOO

如果我想返回以下内容:

AID Name1
--  -----
01  FOO
02  FOO
03  BOO

我写了以下内容:

SELECT TA.AID, TB.Name as Name1 
FROM TB 
INNER JOIN TA on TB.BID = TA.BID1

但是,我无法弄清楚如何返回对应于BID1和BID2的TB.Name.更具体地说,我想返回以下内容:

AID Name1 Name2
--  ----- -----
01  FOO   BOO
02  FOO   LOO
03  BOO   FOO

Answer 1

您可以多次加入:

SELECT TA.AID, tb1.Name AS Name1, tb2.Name AS Name2
FROM TA
LEFT JOIN TB tb1
  ON TA.BID1 = tb1.BID
LEFT JOIN TB tb2
  ON TA.BID2 = tb2.BID;

注意:即使没有匹配LEFT OUTER JOIN,TA也能确保始终获得所有记录.

LiveDemo

Answer 2

只需再使用一个连接

SELECT TA.AID, TB.Name as Name1, T1.Name as Name2
FROM TB 
INNER JOIN TA on TB.BID=TA.BID1
INNER JOIN TB T1 on T1.BID=TA.BID2;