sql 用到了case when

sql 用到了case when

select f.*,
  (
    case f.UsedFlag
      when 1 then d.Name
      when 2 then w.Name
      when 3 then e.Name
      else ''
    end
  ) as Owner,
  b.Name as BuildName,
  p.Name as FlatTpName,
  u.Name as UseTpName
from LFlat f
left outer join LBuilding b on b.ListID=f.BuildingID
left outer join LFlatTp p on p.ListID=f.FlatTpID
left outer join LUseTp  u on u.ListID=f.UseTpID
left join
(
  select A.FlatID, B.TraderID
  from ROrderS A
  left join ROrder B on A.BillID=B.BillID
  where B.VoidFlag=0 and B.StopFlag=0
) as xA on f.ListID=xA.FlatID
left outer join FJoin i on i.FlatID=f.ListID and i.VoidFlag=0 and i.OutFlag=0
left join
(
  select A.FlatID, B.TraderID
  from RContS A
  left join RCont B on A.BillID=B.BillID
  where B.VoidFlag=0 and B.ContClosed=0
) xB on f.ListID=xB.FlatID
left outer join L_Trader d on d.TraderID=xA.TraderID
left outer join L_Trader e on e.TraderID=xB.TraderID
left outer join LOwner w on w.ListID=i.OwnerID

 Order By f.Name