多表连接查询

Question

我有一个主表"master_tbl“，它有以下字段：

m_id(PK)
m_name

两个从表，可以是：

Slave-1 :
---------
sl1_id PK
sl1_name
sl_m_id FK

Slave-2 :
---------
sl2_id PK
sl2_name
sl2_m_id FK

我需要输出，就像在一个查询中一样，匹配记录的详细信息应该显示如下：

m_id     m_name    sl1_name(or sl2_name)

最后一个显示字段应取slave1或Slave2表中匹配记录的名称。

Answer 1

内部连接查询使用

SELECT mt.name, s1.sl1_name, s2.sl2_name FROM master_tbl as mt 
INNER JOIN Slave-1 as s1 ON s1.sl_m_id = mt.m_id
INNER JOIN Slave-2 as s2 ON s2.sl2_m_id = mt.m_id

Answer 2

SELECT m_id, m_name, sl1_name as `sl1_name(or sl2_name)` FROM slave_1 S1 
      INNER JOIN master_tbl M ON S1.sl1_m_id = M.m_id
UNION
SELECT m_id, m_name, sl2_name as `sl1_name(or sl2_name)` FROM slave_2 S2 
      INNER JOIN master_tbl M ON S2.sl2_m_id = M.m_id