Sql 服务器：Select 逐行计算查询

Question

Table PURCHASE(PDate, ItemName, PQty, Rate)

PDate       | ItemName     | PQty  | Rate
============================================
01-04-2015  | Mobile Phone | 06    | 05,000
01-04-2015  | Laptop       | 07    | 30,000
03-04-2015  | Mobile Phone | 03    | 06,000
04-04-2015  | Mobile Phone | 08    | 07,000
04-04-2015  | Laptop       | 03    | 40,000
05-04-2015  | Mobile Phone | 05    | 04,000

Table SALES(SDate, ItemName, SQty)

SDate       | ItemName     | SQty
=================================
02-04-2015  | Mobile Phone | 02
03-04-2015  | Laptop       | 03
03-04-2015  | Mobile Phone | 05
04-04-2015  | Mobile Phone | 07
04-04-2015  | Laptop       | 03
06-04-2015  | Laptop       | 02

SQL

这里我们需要查看 PURCHASE Table 售后的剩余商品及其库存价值 (PQty*Rate)。 (收盘价)
select 查询应该在此处执行此过程。
PURCHASEtable的PQty应该扣除一个一个,从上到下 根据 SALES table's SQty 一个一个, 从上到下 按日期升序排列。
PURCHASE Table 的 PQty 不应变为 0（零），这是当然的。
Incase，如果 PQty 达到零，从 PURCHASE Table's[= 的下一行中扣除 SALES 剩余的 SQty 52=] 列表中的 PQty。

如果没有更多行可用，最后一行可能为负值。

tables 之间的条件完成 WHERE SALES.ItemName LIKE PURCHASE.ItemName

Table EXPECTED SELECT QUERY RESULT (Date, ItemName, Qty, Rate, ProductValue)

PDate | ItemName | PQty | Rate | ProductValue =========================================================== 01-04-2015 | Mobile Phone | 00 | 05,000 | 0.00 01-04-2015 | Laptop | 00 | 30,000 | 0.00 03-04-2015 | Mobile Phone | 00 | 06,000 | 0.00 04-04-2015 | Mobile Phone | 03 | 07,000 | 21,000.00 04-04-2015 | Laptop | 02 | 40,000 | 80,000.00 05-04-2015 | Mobile Phone | 05 | 04,000 | 20,000.00

我该如何解决这个问题？

Answer 1

SELECT PDate, ItemName, MPQty, PQty, ISNULL(SQty,0) AS SQty,
ISNULL((CASE WHEN SQTY>=PQty THEN 0 WHEN (SQty+MPQty)>PQty THEN PQty-SQty ELSE MPQty END),0) AS Qty, Rate,
(ISNULL((CASE WHEN SQTY>=PQty THEN 0 WHEN (SQty+MPQty)>PQty THEN PQty-SQty ELSE MPQty END),0)*Rate) AS PValue FROM
(SELECT P.PDate AS PDate, P.ItemName AS ItemName, P.PQty AS MPQty,
(SELECT SUM(P1.PQty) FROM PURCHASE P1 WHERE P1.ItemName=P.ItemName AND P1.PDate<=P.PDate) AS PQty,
(SELECT SUM(S1.SQty) FROM SALES S1 WHERE S1.ItemName=P.ItemName) AS SQty,    
P.Rate AS Rate FROM PURCHASE P)X ORDER BY Pdate

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