left join、right join 与inner join的区别
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一句话 道出关键select * from A a left join B b on a.id = b.id左连接 以左表为基准,可以理解为将两张表的数据连接起来,只是按照A表的数据,将两张表拼接起来,B表不够的字段或者不满足a.id=b.id的用Null展示。select * from A a right join B b on a.id = b.id右连接 以右表为基准,可以理解为将两张表的数据连接起来,只是按照B表的数据,将两张表拼接起来,A表不够的字段或者不满足a.id=b.id的用Null展示。select * from A a inner join B b on a.id = b.id内连接 需要以两张表为基准,只有同时满足a.id = b.id的数据才会展示出来。
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