從2欄消費值

Question

我想弄清楚如何做一種「消費」查詢，其中INT值列（X）從另一個INT列（Y）中減去，直到它達到0，然後停止。 DesiredResult和DesiredResultExplanation這一列僅用於參考正在執行的數學。這發生在DESC日期順序（未來消耗回當前）

我最初的方法是使用窗口功能，但問題是一旦值（Y）達到0，它需要停止執行運行總數。使用CTE也有類似的問題。

如果更改表格結構將有所幫助，可以這樣做。

版本：SQL Server 2014或更高版本

謝謝！

DECLARE @test TABLE 
(
ID INT IDENTITY (1,1) 
,PeriodDate DATE 
,X INT 
,Y INT 
,DesiredResult INT 
,DesiredResultExplanation VARCHAR(100) 
) 

INSERT INTO @test VALUES ('2017-05-01', 100,0, 100,'Nothing left to subtract. Value is unchanged') 
INSERT INTO @test VALUES ('2017-05-08', 200,0, 200,'Nothing left to subtract. Value is unchanged') 
INSERT INTO @test VALUES ('2017-05-15', 300,0, 100,'300 - 200 = 100 (Orig -1100 has been consumed)') 
INSERT INTO @test VALUES ('2017-05-22', 400,0,-200,'400 - 600 = -200 ') 
INSERT INTO @test VALUES ('2017-05-29', 500,-1100,-600, '500 - 1100 = -600') 

SELECT * 
FROM @test 
ORDER BY PeriodDate DESC 

Answer 1

DEMO

WITH cte as (
    SELECT *, 
      SUM(X) OVER (ORDER BY PeriodDate DESC) accumulated 
    FROM @test 
), parameter as (
    SELECT 1100 as startY 
)  
SELECT *, 
     CASE WHEN accumulated <= startY 
      THEN accumulated - startY 
      WHEN LAG(accumulated) OVER (ORDER BY PeriodDate DESC) < startY 
      THEN accumulated - startY 
      ELSE X 
     END as newDesire 
FROM cte 
CROSS JOIN parameter 
ORDER BY PeriodDate DESC; 

輸出

​​

編輯：您可以更改LAG條件與

WHEN accumulated - X < startY