SQL INNER JOIN ON table1.column1 = table2.column2或ON ..？

Question

如果要通过INNER JOIN选择数据库，但使用2 ON和ON之间的OR，则使用什么SQL脚本。

这是我的错误脚本

SELECT * 
FROM user
INNER JOIN friend ON friend.id1_friend = user.id_user 
                  OR ON friend.id2_friend = user.id_user
WHERE id_user != '$_SESSION[user]' 
  AND friend_status != '2'
ORDER BY id_user DESC

Answer 1

一张桌子只能使用一次。 您刚刚提出的条件或其他条件。

 SELECT*FROM user
INNER JOIN friend ON 
(friend.id1_friend=user.id_user OR friend.id2_friend=user.id_user)
WHERE id_user != $_SESSION[user]
AND friend_status != '2'
ORDER BY id_user DESC

Answer 2

SELECT * -- this is not smart
  FROM user u
  JOIN friend f
    ON u.id_user IN(f.id1_friend,f.id2_friend)
 WHERE u.id_user != '$_SESSION[user]' -- this is not safe
   AND f.friend_status != 2
 ORDER 
    BY u.id_user DESC