SQL Server - assign value to a field based on a running total - sql-server

Question

For a customer, I'm sending through an XML file to another system, the sales orders and I sum the quantities for each item across all sales orders lines (e.g.: if I have "ItemA" in 10 sales orders with different quantities in each one, I sum the quantity and send the total).
In return, I get a response whether the requested quantities can be delivered to the customers or not. If not, I still get the total quantity that can be delivered. However, could be situations when I request 100 pieces of "ItemA" and I cannot deliver all 100, but 98. In cases like this, I need to distribute (to UPDATE a custom field) those 98 pieces FIFO, according to the requested quantity in each sales order and based on the registration date of each sales order.
I tried to use a WHILE LOOP but I couldn't achieve the desired result. Here's my piece of code:
DECLARE #PickedQty int
DECLARE #PickedERPQty int
DECLARE #OrderedERPQty int=2
SET #PickedQty =
WHILE (#PickedQty>0)
BEGIN
SET #PickedERPQty=(SELECT CASE WHEN #PickedQty>#OrderedERPQty THEN #OrderedERPQty ELSE #PickedQty END)
SET #PickedQty=#PickedQty-#PickedERPQty
PRINT #PickedQty
IF #PickedQty>=0
BEGIN
UPDATE OrderLines
SET UDFValue2=#PickedERPQty
WHERE fDocID='82DADC71-6706-44C7-9B78-7FCB55D94A69'
END
IF #PickedQty <= 0
BREAK;
END
GO
Example of response
I requested 35 pieces but only 30 pieces are available to be delivered. I need to distribute those 30 pieces for each sales order, based on requested quantity and also FIFO, based on the date of the order. So, in this example, I will update the RealQty column with the requested quantity (because I have stock) and in the last one, I assign the remaining 5 pieces.
ord_Code CustOrderCode Date ItemCode ReqQty AvailQty RealQty
----------------------------------------------------------------------------
141389 CV/2539 2018-11-25 PX085 10 30 10
141389 CV/2550 2018-11-26 PX085 5 30 5
141389 CV/2563 2018-11-27 PX085 10 30 10
141389 CV/2564 2018-11-28 PX085 10 30 5
Could anyone give me a hint? Thanks

Answer 1

This might be more verbose than it needs to be, but I'll leave it to you to skinny it down if that's possible.
Set up the data:
DECLARE #OrderLines TABLE(
ord_Code INTEGER NOT NULL
,CustOrderCode VARCHAR(7) NOT NULL
,[Date] DATE NOT NULL
,ItemCode VARCHAR(5) NOT NULL
,ReqQty INTEGER NOT NULL
,AvailQty INTEGER NOT NULL
,RealQty INTEGER NOT NULL
);
INSERT INTO #OrderLines(ord_Code,CustOrderCode,[Date],ItemCode,ReqQty,AvailQty,RealQty) VALUES (141389,'CV/2539','2018-11-25','PX085',10,0,0);
INSERT INTO #OrderLines(ord_Code,CustOrderCode,[Date],ItemCode,ReqQty,AvailQty,RealQty) VALUES (141389,'CV/2550','2018-11-26','PX085', 5,0,0);
INSERT INTO #OrderLines(ord_Code,CustOrderCode,[Date],ItemCode,ReqQty,AvailQty,RealQty) VALUES (141389,'CV/2563','2018-11-27','PX085',10,0,0);
INSERT INTO #OrderLines(ord_Code,CustOrderCode,[Date],ItemCode,ReqQty,AvailQty,RealQty) VALUES (141389,'CV/2564','2018-11-28','PX085',10,0,0);
DECLARE #AvailQty INTEGER = 30;
For running totals, for SQL Server 20012 and up anyway, SUM() OVER is the preferred technique so I started off with some variants on that. This query brought in some useful numbers:
SELECT
ol.ord_Code,
ol.CustOrderCode,
ol.Date,
ol.ItemCode,
ol.ReqQty,
#AvailQty AS AvailQty,
SUM(ReqQty) OVER (PARTITION BY ord_Code ORDER BY [Date]) AS TotalOrderedQty,
#AvailQty-SUM(ReqQty) OVER (PARTITION BY ord_Code ORDER BY [Date]) AS RemainingQty
FROM
#OrderLines AS ol;
Then I used the RemainingQty to do a little math. The CASE expression is hairy, but the first step checks to see if the RemainingQty after processing this row will be positive, and if it is, we fulfill the order. If not, we fulfill what we can. The nested CASE is there to stop negative numbers from coming into the result set.
SELECT
ol.ord_Code,
ol.CustOrderCode,
ol.Date,
ol.ItemCode,
ol.ReqQty,
#AvailQty AS AvailQty,
SUM(ReqQty) OVER (PARTITION BY ord_Code ORDER BY [Date]) AS TotalOrderedQty,
#AvailQty-SUM(ReqQty) OVER (PARTITION BY ord_Code ORDER BY [Date]) AS RemainingQty,
CASE
WHEN (#AvailQty-SUM(ReqQty) OVER (PARTITION BY ord_Code ORDER BY [Date])) > 0
THEN ol.ReqQty
ELSE
CASE
WHEN ol.ReqQty + (#AvailQty-SUM(ReqQty) OVER (PARTITION BY ord_Code ORDER BY [Date])) > 0
THEN ol.ReqQty + (#AvailQty-SUM(ReqQty) OVER (PARTITION BY ord_Code ORDER BY [Date]))
ELSE 0
END
END AS RealQty
FROM
#OrderLines AS ol
Windowing functions (like SUM() OVER) can only be in SELECT and ORDER BY clauses, so I had to do a derived table with a JOIN. A CTE would work here, too, if you prefer. But I used that derived table to UPDATE the base table.
UPDATE Lines
SET
Lines.AvailQty = d.AvailQty
,Lines.RealQty = d.RealQty
FROM
#OrderLines AS Lines
JOIN
(
SELECT
ol.ord_Code,
ol.CustOrderCode,
ol.Date,
ol.ItemCode,
#AvailQty AS AvailQty,
CASE
WHEN (#AvailQty-SUM(ReqQty) OVER (PARTITION BY ord_Code ORDER BY [Date])) > 0
THEN ol.ReqQty
ELSE
CASE
WHEN ol.ReqQty + (#AvailQty-SUM(ReqQty) OVER (PARTITION BY ord_Code ORDER BY [Date])) > 0
THEN ol.ReqQty + (#AvailQty-SUM(ReqQty) OVER (PARTITION BY ord_Code ORDER BY [Date]))
ELSE 0
END
END AS RealQty
FROM
#OrderLines AS ol
) AS d
ON d.CustOrderCode = Lines.CustOrderCode
AND d.ord_Code = Lines.ord_Code
AND d.ItemCode = Lines.ItemCode
AND d.Date = Lines.Date;
SELECT * FROM #OrderLines;
Results:
+----------+---------------+---------------------+----------+--------+----------+---------+
| ord_Code | CustOrderCode | Date | ItemCode | ReqQty | AvailQty | RealQty |
+----------+---------------+---------------------+----------+--------+----------+---------+
| 141389 | CV/2539 | 25.11.2018 00:00:00 | PX085 | 10 | 30 | 10 |
| 141389 | CV/2550 | 26.11.2018 00:00:00 | PX085 | 5 | 30 | 5 |
| 141389 | CV/2563 | 27.11.2018 00:00:00 | PX085 | 10 | 30 | 10 |
| 141389 | CV/2564 | 28.11.2018 00:00:00 | PX085 | 10 | 30 | 5 |
+----------+---------------+---------------------+----------+--------+----------+---------+
Play with different available qty values here: https://rextester.com/MMFAR17436