（A加入B）加入（C加入d）

Question

我想使特定顺序的JOIN的

SELECT * 
FROM (lives_in as t1 NATURAL JOIN preferences p1) l1 
JOIN (lives_in t2 NATURAL JOIN preferences p2) l2 
ON l1.dormid = l2.dormid 

返回一个错误。

任何人都可以帮忙吗？非常感谢！

Answer 1

你的别名查询缺少SELECT条款，所以试试这个：

SELECT * 
FROM (
    select * -- added this 
    FROM lives_in as t1 
    NATURAL JOIN preferences p1) l1 
JOIN (
    select * -- added this 
    FROM lives_in t2 
    NATURAL JOIN preferences p2) l2 
ON l1.dormid = l2.dormid 

Answer 2

连接顺序对结果无关紧要。你可能想要这样的事情：

SELECT * 
FROM lives_in t1 
NATURAL JOIN preferences p1 ON p1.some_id = t1.id 
NATURAL JOIN preferences p2 ON p2.some_id = t1.id 

此外，大多数人称它为INNER JOIN，而不是NATURAL JOIN，顺便说一句。

Answer 3

希望它会很有帮助。

SELECT * 
FROM (
select * from lives_in as t1 NATURAL JOIN preferences p1 
) l1 
JOIN (
select * from lives_in t2 NATURAL JOIN preferences p2 
) l2 
ON l1.dormid = l2.dormid