一个学生可以注册多个班级,我想列出没有注册的学生,但是我找不到我错在哪里。
下面是我的代码,列出了类中的内容:
SELECT users.id as id, users.rank, users.name_surname, users.status
FROM userClasses,users
WHERE userClasses.user = users.id
AND userClasses.classes = 2
下面是我的代码,其中列出了未注册到类的对象:
SELECT users.id as id, users.rank, users.name_surname, users.status
FROM userClasses,users
WHERE userClasses.user = users.id
AND userClasses.classes <> 2
你能帮忙吗?
我也试过这个代码,它没有给予正确的结果。
SELECT users.* FROM
( SELECT users.*, userClasses.classes
FROM users
LEFT JOIN userClasses
ON users.id = userClasses.user
WHERE ((userClasses.classes <> 2)
OR (userClasses.classes IS NULL)) AND users.`rank`=1 )
users
LEFT JOIN classes
ON users.classes = classes.id;
1条答案
按热度按时间hrirmatl1#