如何根据条件连接两个表？

Question

一共有三个表A,B,C

一个表的列是名称、ID、地址

B表列是ID,Address,School

C表的列是School,address,cafe

如果名称='A' 然后表 A 和表 B 将根据 A.ID =B.ID 进行连接

如果名称='B'

那么表 A 和表 B 将根据 A.ID =B.ID 和 A.Address=B.Address 加入

这个结果与表 C 连接

Answer 1

使用OR 和AND 运算符模拟ON 子句中的if 条件。试试这个Join

SELECT *
FROM   A
       INNER JOIN B
               ON ( A.name = 'A'
                    AND A.ID = B.ID )
                   OR ( A.Name = 'B'
                        AND A.ID = B.ID
                        AND A.Address = B.Address )
       INNER JOIN C
               ON B.school = C.school 

Answer 2

你可以试试下面的代码：

SELECT * 
FROM A
INNER JOIN B 
  ON (   (B.Name = 'A' AND A.ID = B.ID) 
      OR (B.Name = 'B' AND A.ID = B.ID AND A.Address=B.Address)
     )

您现在可以将结果与表 C 连接起来

谢谢

Answer 3

假设 A.Name 是 A 或 B：

SELECT *
FROM   A
  JOIN B ON ( A.ID = B.ID )
            AND ( A.Name = 'A' OR A.Address = B.Address )
  JOIN C ON B.school = C.school 

Answer 4

SELECT * FROM A INNER JOIN B
    ON A.ID = B.ID
    INNER JOIN C
    ON B.SCHOOL = C.SCHOOL
WHERE A.NAME = 'A'
UNION ALL
SELECT * FROM A INNER JOIN B
    ON A.ID =B.ID and A.Address=B.Address
    INNER JOIN C
    ON B.SCHOOL = C.SCHOOL
    WHERE A.NAME = 'B'

这可能有效