SQL服务器加入

Question

我需要在以下情况下

Table One 
Col A 
Col B 
Col C1 
Col C2 
Col C3 

Table Two 
Col C 
Col D 

我需要加入[一]与[二]，并得到One.A和Two.D作为我的输出连接两个表的帮助。

这里是连接逻辑：

加入[一] .C1 = [二] .C如果不匹配，我需要加入[大]≥C2 = Two.C如果再没有匹配加盟[大]≥C3 = [二] .C

Answer 1

您需要COALESCE()：

SELECT DISTINCT 
    COALESCE(One1.A, One2.A, One3.A) AS A, 
    D 
FROM 
    Two 
    LEFT JOIN One AS One1 ON 
     Two.C = One1.C1 
    LEFT JOIN One AS One2 ON 
     Two.C = One2.C2 
    LEFT JOIN One AS One3 ON 
     Two.C = One3.C3; 

Answer 2

尝试此查询：

SELECT 
one.A as oneA, 
two.D as twoD 
FROM 
One one 
INNER JOIN Two two ON one.C1 = two.C 
OR one.C1 = two.C2 
OR one.C3 = two.C;