sql Left Join 右表取一条数据，三种方式

一、（Oracle中已驗證OK）

left join

(select l.* from 
  (select RealName,CompanyId,row_number() over (partition by CompanyId order by id desc) as rownum1 from vm_User WHERE IsAdmin=1) l
   where l.rownum1 = 1 )  w

二、left join (select MAX(RealName),CompanyId, from vm_User GROUP BY CompanyId) W

三、

用OUTER APPLY
select b.* FROM a表 a
OUTER APPLY
(select TOP(1) * from b表 WHERE [Name] = a.[AName] ORDER BY BNo desc) b
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