mysql - (A 加入 B) 加入 (C 加入 D)

Question

我想制定特定的 JOIN 顺序

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

返回错误。

任何人都可以帮忙吗？非常感谢！

Answer 1

您的别名查询缺少一个SELECT子句，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

连接的顺序与结果无关。你可能想要这样的东西：

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，大多数人称其为 INNER JOIN，而不是 NATURAL JOIN，顺便说一句。

Answer 3

希望它会有所帮助。

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