找到最後的價格是從目前的價格不同

Question

我有銷售交易在SQL Server表是這樣的：

ItemNumber, TrxDate, UnitPrice 
ABC, 1/1/2013, 10.00 
ABC, 2/1/2013, 10.00 
ABC, 3/1/2013, 13.00 
ABC, 4/1/2013, 14.00 
ABC, 5/1/2013, 14.00 
XYZ, 1/1/2013, 18.00 
XYZ, 2/1/2013, 18.00 
XYZ, 3/1/2013, 20.00 
XYZ, 4/1/2013, 20.00 
XYZ, 5/1/2013, 20.00 

我需要一個存儲過程來產生輸出看起來像這樣

ItemNumber, LastPrice, PriorPrice 
ABC, 14.00, 13.00 
XYZ, 20.00, 18.00 

Answer 1

您可以使用lag()功能首先發現做到這一點，當價格變動：

select ItemNumber, 
     max(case when seqnum = 1 then Price end) as LastPrice, 
     max(case when seqnum = 2 then Price end) as PriorPrice 
from (select t.*, row_number() over (partition by ItemNumber order by TrxDate desc) as seqnum 
     from (select t.*, 
        lag(Price) over (partition by ItemNumber order by TrxDate) as PrevPrice 
      from t 
      ) t 
     where Price <> PrevPrice or PrevPrice is NULL 
    ) t 
group by ItemNumber; 

時滯僅開始可用SQL Server 2012的

如果沒有lag()，則可以做同樣的事情用一個相關子查詢：

select ItemNumber, 
     max(case when seqnum = 1 then Price end) as LastPrice, 
     max(case when seqnum = 2 then Price end) as PriorPrice 
from (select t.*, row_number() over (partition by ItemNumber order by TrxDate) as seqnum 
     from (select t.*, 
        (select top 1 t2.Price 
        from t t2 
        where t.ItemNumber = t2.ItemNumber and 
          t.TrxDate > t2.TrxDate 
        order by t2.TrxDate desc 
        ) as PrevPrice 
      from t 
      ) t 
     where Price <> PrevPrice or PrevPrice is NULL 
    ) t 
group by ItemNumber; 

Answer 2

Assmunig的SQL Server 2005+：

;WITH CTE AS 
(
    SELECT *, 
      RN=ROW_NUMBER() OVER(PARTITION BY ItemNumber ORDER BY TrxDate DESC) 
    FROM ( SELECT ItemNumber, 
        MAX(TrxDate) TrxDate, 
        UnitPrice 
      FROM YourTable 
      GROUP BY ItemNumber, 
        UnitPrice) A 
) 
SELECT ItemNumber, 
     MIN(CASE WHEN RN = 1 THEN UnitPrice END) LastPrice, 
     MIN(CASE WHEN RN = 2 THEN UnitPrice END) PriorPrice 
FROM CTE 
GROUP BY ItemNumber