作业帮select * from a right join b on a.id=b.id; select * from a join b on a.id=b.id; 有什么区别啊?我怎么感觉第二句完全能代替第一句,那个左右连接,全连接没什么用啊.请哪位高手能讲讲具体的区别!
来源：学生作业帮助网 编辑：作业帮 时间：2024/11/16 10:43:41
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select * from a right join b on a.id=b.id; select * from a join b on a.id=b.id; 有什么区别啊?我怎么感觉第二句完全能代替第一句,那个左右连接,全连接没什么用啊.请哪位高手能讲讲具体的区别!
select * from a right join b on a.id=b.id; select * from a join b on a.id=b.id; 有什么区别啊?
我怎么感觉第二句完全能代替第一句,那个左右连接,全连接没什么用啊.请哪位高手能讲讲具体的区别!
select * from a right join b on a.id=b.id; select * from a join b on a.id=b.id; 有什么区别啊?我怎么感觉第二句完全能代替第一句,那个左右连接,全连接没什么用啊.请哪位高手能讲讲具体的区别!
假如.a id不存在.你第一种方法可以取出来,但是第二哥就会出错.
right的意识就是以第二个表为主,第一个表不存在也会输出
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