SQL Running Subtraction

Question

I have a result set as below:

Item    ExpectedQty  ReceivedQty  Short
Item01  30           45           5
Item01  20           45           5

Item02  40             


        

Answer 1

One part of the problem is to get the running totals of expected item qunatities. For that you'd need a way to distinguish rows with same items from each other and a rule for the order of discharging same item quantities.

For the purpose of my attempt at solving your problem I'm going to assume there's a timestamp column whose values provide the order of discharge and are unique within same item groups.

Here's the sample data definition I was testing my solution on:

CREATE TABLE TableA (Item varchar(50), ExpectedQty int, Timestamp int);
INSERT INTO TableA
SELECT 'Item01', 30, 1 UNION ALL
SELECT 'Item01', 20, 2 UNION ALL
SELECT 'Item02', 40, 1 UNION ALL
SELECT 'item03', 50, 1 UNION ALL
SELECT 'item03', 30, 2 UNION ALL
SELECT 'item03', 20, 3;

CREATE TABLE TableB (Item varchar(50), ReceivedQty int);
INSERT INTO TableB
SELECT 'Item01', 45 UNION ALL
SELECT 'Item02', 38 UNION ALL
SELECT 'item03', 90;

And here's my solution:

SELECT
  Item,
  ExpectedQty,
  ReceivedQty = CASE
    WHEN RemainderQty >= 0 THEN ExpectedQty
    WHEN RemainderQty < -ExpectedQty THEN 0
    ELSE RemainderQty + ExpectedQty
  END,
  Short = CASE
    WHEN RemainderQty >= 0 THEN 0
    WHEN RemainderQty < -ExpectedQty THEN ExpectedQty
    ELSE ABS(RemainderQty)
  END
FROM (
  SELECT
    a.Item,
    a.ExpectedQty,
    RemainderQty = b.ReceivedQty - a.RunningTotalQty
  FROM (
    SELECT
      a.Item,
      a.Timestamp,
      a.ExpectedQty,
      RunningTotalQty = SUM(a2.ExpectedQty)
    FROM TableA a
      INNER JOIN TableA a AS a2 ON a.Item = a2.Item AND a.Timestamp >= a2.Timestamp
    GROUP BY
      a.Item,
      a.Timestamp,
      a.ExpectedQty
  ) a
    INNER JOIN TableB b ON a.Item = b.Item
) s

Answer 2

select a.Item, a.ExpectedQty,b.ReceivedQty, (a.ExpectedQty - b.ReceivedQty) as 'Short' from a join b on a.Item = b.Item

Answer 3

SELECT  a.ExpectedQty,
    b.ReceivedQty,
    CASE WHEN b.ReceivedQty < a.ExpectedQty
         THEN b.ReceivedQty - a.ExpectedQty
         ELSE 0
    END Short
FROM    dbo.a a
INNER JOIN dbo.b b
ON      a.ItemId = b.ItemId