左連接查詢的思考

　　左連接查詢

　　select  uGroup_IduGroup_NamelUser_IdlPosition_Id

　　from usergroup u

　　left join (select * from UserGroupLink where User_Id=admin and company_id=) as l  on uGroup_Id=lGroup_Id;

　　as可以省略

　　注意寫成以下這樣就不可以了

　　select  uGroup_IduGroup_NamelUser_IdlPosition_Id

　　from usergroup u

　　left join select  * from  (select * from UserGroupLink where User_Id=admin and company_id=) as l  on uGroup_Id=lGroup_Id;

From:http://tw.wingwit.com/Article/program/Oracle/201311/18324.html