兩個表join 連接，去掉重復的數據

-------distinct 去重復查詢

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

 

--------解釋一下不用distinct 去重復查詢語句

Select * from (Select max(不重復的字段就行) as roleid,要去重復字段名 From 數據表 Where  條件 Group by   要去重復字段名) as A join 數據庫表 on 條件