Question

我想制作JOIN的具体顺序

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。

任何人都可以提供帮助？非常感谢！

Answer 1

您的别名查询缺少SELECT子句，请尝试以下操作：

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，大多数人称之为INNER JOIN，而非天然加入，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

（A加入B）加入（C加入D）

3 个答案: