连接中是否包含SQL Case / IF语句？

Question

我有以下语句，尽管输出以某种方式起作用，但我正在尝试以无法获得结果的方式对要获取客户，组或主组数据的联接进行布局一堆用于销售代表和折扣代码的空白列，这些代码将根据以下联接与该商品绑定。最终，这将在PowerBI中进行，并且我尝试将一个Master Group，Group或Cust填充到所有适当的位置（客户可以属于一个组或Master Group，而这些组可以属于Master Group），然后仅得到一个销售代表或折扣代码列。

SELECT top 5             
P.Item#                         AS Item_No
, I.Description                 AS Item_Desc
, I."Class Description"         AS Class_Desc
, I."Vendor Name"               AS Vendor_Name
, I."Landed Cost"               AS Landed_Cost
, I."Current Price 1"           AS Base_Price
, P."Price Exception"           AS Locked_Price
, P."From DTTM"                 AS Locked_From_DTTM
, P."To DTTM"                   AS Locked_To_DTTM
, P.Customer#                   AS Customer_No
, C1."Ship Name"                AS Customer_Name
, C2."Group Name"               AS Customer_Group
, C3."Master Group Name"        AS Customer_Master_Group
, C1."Sales Rep Name"           AS Sales_Rep
, C2."Sales Rep Name"           AS Sales_Rep_Group
, C3."Sales Rep Name"           AS Sales_Rep_Master_Group
, C1."Discount Code"            AS Discount_Code    
FROM "Promotion Pricing" P           
LEFT JOIN ItemStat I
     ON P.Item# = I.Item#
LEFT JOIN CustStats C1
     ON P.Customer# = C1.Cust#
LEFT JOIN CustStats C2
     ON P.Group# = C2."Cust Group#"
LEFT JOIN CustStats C3
     ON P.Group# = C3."Master Group#"