MySQL Left Join不止一次

Question

我有一个像这样的表：

数据：

id | state | more
-----------------
1  | 1     | ...
2  | 2     | ...
3  | 1     | ...

和州：

id | state
----------
1  | Open
2  | Closed

如果我这样做

SELECT states.state FROM data LEFT JOIN states ON data.state = states.id

我收到了

state
-----
Open
Closed
Open

到目前为止一切顺利。我想做的事情（没有成功）是，如果我有一个像这样的数据表：

id | state | state2 | more
--------------------------
1  | 1     | 2      | ...
2  | 2     | 1      | ...
3  | 1     | 1      | ...

我如何获得：

state  | state 2
----------------
Open   | Closed 
Closed | Open
Open   | Open

Answer 1

SELECT states.state, states2.state
FROM data
LEFT JOIN states as states ON data.state = states.id
LEFT JOIN states as states2 ON data.state2 = states2.id

Answer 2

只需使用其他LEFT JOIN和alias

即可

SELECT 
   s1.state AS state1
   s2.state AS state2 
FROM data d
LEFT JOIN states s1 ON d.state = s1.id
LEFT JOIN states s2 ON d.state2 = s2.id

Answer 3

你需要做另一个左连接

SELECT 
   s1.state AS state1,
   s2.state AS state2 
FROM data d
LEFT JOIN states s1 ON d.state = s1.id
LEFT JOIN states s2 ON d.state2 = s2.id