两个表join 连接，去掉重复的数据
-------distinct 去重复查询select * from accounts acc join (select distinct accid from roles) r on r.accid=acc.ID
-----不需要distinct select * from (select MAX(ID)roleid,accid from roles group by accid) rr join (select * from accounts) acc on acc.ID=rr.accid
--------解释一下不用distinct 去重复查询语句
Select * from (Select max(不重复的字段就行) as roleid,要去重复字段名 From 数据表 Where 条件 Group by 要去重复字段名) as A join 数据库表 on 条件
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