Question

我必须得到A.Ref_id，B.Ref_id和B_Id的Ref_id

Table A_B having Column_A_ID and Column_B_ID
Table A having ID, Ref_id, Name, B_Id (This is the B.ID from table B)
Table B having ID, Ref_id, Name

目前我正在进行以下查询

SELECT A.Ref_id as A_Ref_Id,  B.Ref_id as B_Ref_Id, B_Id
FROM A_B
JOIN A on A_B.Column_A_ID = A.Id 
JOIN B on A_B.Column_B_ID = B.Id 
JOIN B AS Main_B on B.id = A.B_id;

通过此查询，我正确地显示了A.Ref_Id和B.Ref_Id列，因为它们显示了相关的Ref_id，但对于B_Id我想要{{1}而且它显示Ref_id而不是。

Answer 1

到目前为止，我看到上次联接的ON条件必须使用表B的别名：

SELECT A.Ref_id as A_Ref_Id,  B.Ref_id as B_Ref_Id, B_Id
FROM A_B
JOIN A on A_B.Column_A_ID = A.Id 
JOIN B on A_B.Column_B_ID = B.Id 
JOIN B AS Main_B on Main_B.id = A.B_id;

顺便说一句，在sqlFiddle中有一些例子可能会更有帮助

Answer 2

您想要这个（对吗？）：B.Ref_id行中B.ID = A.B_Id的值，而此行依次为A.ID=A_B.Column_A_ID。以及A_B中每一行的全部内容：

SELECT A.Ref_id as A_Ref_id, B.Ref_id as B_Ref_id, Main_B.Ref_id
FROM A_B
JOIN A ON A_B.Column_A_ID = A.Id 
JOIN B ON A_B.Column_B_ID = B.Id 
JOIN B AS Main_B on Main_B.id = A.B_id;

（@Mojtaba提出的重要修正的最后一行代码）

来自连接三个表

2 个答案: