（A加入B）加入（C加入d）

Question

我想使特定順序的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 

返回一個錯誤。

任何人都可以幫忙嗎？非常感謝！

Answer 1

你的別名查詢缺少SELECT條款，所以試試這個：

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

連接順序對結果無關緊要。你可能想要這樣的事情：

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，大多數人稱它爲INNER JOIN，而不是NATURAL JOIN，順便說一句。

Answer 3

希望它會很有幫助。

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