SQL Server : filling in sparse values - sql-server

Question

Need help with SQL Server; what will be the easiest way to update the missing begin and end inventory values? Values shown are verified numbers for that week.
+------+--------+-------+----------+-----+
| Week | ItemNr | Begin | Increase | End |
+------+--------+-------+----------+-----+
| 1 | 1001 | 100 | -10 | 90 |
| 2 | 1001 | | 0 | |
| 3 | 1001 | 90 | 0 | 90 |
| 4 | 1001 | | 20 | |
| 5 | 1001 | | 100 | |
| 6 | 1001 | | -20 | |
| 7 | 1001 | | 0 | |
| 8 | 1001 | 200 | 10 | 210 |
| 9 | 1001 | | 0 | |
| 10 | 1001 | | -50 | -50 |
| 11 | 1001 | | 0 | |
+------+--------+-------+----------+-----+
if Begin is NULL then previous week End
END = Begin + Increase

Answer 1

A couple of window functions gets you the result. ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW is the default scope when you specify an ORDER BY in the OVER clause, however, as the other window function has it explicitly stated and doesn't use the default scope, I felt it was important to show; as you can see the difference.
WITH VTE AS(
SELECT *
FROM (VALUES ( 1,1001,100,-10),
( 2,1001,NULL, 0),
( 3,1001, 90, 0),
( 4,1001,NULL, 20),
( 5,1001,NULL,100),
( 6,1001,NULL,-20),
( 7,1001,NULL, 0),
( 8,1001,200, 10),
( 9,1001,NULL, 0),
(10,1001,NULL,-50),
(11,1001,NULL, 0)) V(Week, ItemNr, [Begin],Increase))
SELECT Week,
ItemNr,
ISNULL([Begin],S.Starting + SUM(Increase) OVER (PARTITION BY ItemNr ORDER BY Week ROWS BETWEEN UNBOUNDED PRECEDING AND 1 PRECEDING)) AS [Begin],
Increase,
S.Starting + SUM(Increase) OVER (PARTITION BY ItemNr ORDER BY Week ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW) AS [End]
FROM VTE V
CROSS APPLY (SELECT TOP 1 [Begin] AS Starting
FROM VTE ca
WHERE ca.ItemNr = V.ItemNr
ORDER BY Week ASC) S;
Note: This appears to be some kind of stock system. it's worth noting that this doesn't take into account that the stock level could go wrong. For example, say an item is stolen; the value of [End] and [Begin] (when it has a value of NULL) would be wrong in those events. If this needs to be taken into consideration, then we need to know this in the question.
Edit: Solution to cater for "lost" stock. With this, this takes the last "known" value for the stock and aggregates. So, for this example, in Week 1, although 10 items were "sold", the start of the week 2 shows the beginning value as 35. This means that 5 items are missing (stolen?). This there needs to effect all stock levels going forward. Thus you get:
WITH VTE AS(
SELECT *
FROM (VALUES ( 1,1001,100,-10),
( 2,1001,NULL, 0),
( 3,1001, 90, 0),
( 4,1001,NULL, 20),
( 5,1001,NULL,100),
( 6,1001,NULL,-20),
( 7,1001,NULL, 0),
( 8,1001,200, 10),
( 9,1001,NULL, 0),
(10,1001,NULL,-50),
(11,1001,NULL, 0),
(1,1002,50,-10),
(2,1002,35,0),--Begin value lowered. Some items went "missing"
(3,1002,NULL,5),
(4,1002,40,10)) V(Week, ItemNr, [Begin],Increase))
SELECT Week,
ItemNr,
[Begin],
Increase,
LastKnown,
WeekKnown,
ISNULL([Begin],S.LastKnown + SUM(Increase) OVER (PARTITION BY ItemNr, WeekKnown ORDER BY Week ROWS BETWEEN UNBOUNDED PRECEDING AND 1 PRECEDING)) AS ActualBegin,
ISNULL([Begin],S.LastKnown + SUM(Increase) OVER (PARTITION BY ItemNr, WeekKnown ORDER BY Week ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW)) AS [End]
FROM VTE V
CROSS APPLY (SELECT TOP 1 [Begin] AS LastKnown, Week AS WeekKnown
FROM VTE ca
WHERE ca.ItemNr = V.ItemNr
AND ca.Week <= V.Week
AND ca.[Begin] IS NOT NULL
ORDER BY Week DESC) S
ORDER BY V.ItemNr, V.Week;

Answer 2

Here is another way too
SELECT T1.Week,
T1.ItemNr,
CASE WHEN T1.[Begin] IS NULL THEN
(SELECT MAX([Begin]) + SUM(Increase) FROM #T WHERE Week < T1.Week AND ItemNr = T1.ItemNr)
ELSE
T1.[Begin]
END [Begin],
T1.Increase,
CASE WHEN T1.[Begin] IS NULL THEN
(SELECT MAX([Begin]) + SUM(Increase) FROM #T WHERE Week < T1.Week AND ItemNr = T1.ItemNr)
ELSE
T1.[Begin]
END + T1.Increase [End]
FROM #T T1;
Returns:
+------+--------+-------+----------+-----+
| Week | ItemNr | Begin | Increase | End |
+------+--------+-------+----------+-----+
| 1 | 1001 | 100 | -10 | 90 |
| 2 | 1001 | 90 | 0 | 90 |
| 3 | 1001 | 90 | 0 | 90 |
| 4 | 1001 | 90 | 20 | 110 |
| 5 | 1001 | 110 | 100 | 210 |
| 6 | 1001 | 210 | -20 | 190 |
| 7 | 1001 | 190 | 0 | 190 |
| 8 | 1003 | 200 | 10 | 210 |
| 9 | 1003 | 210 | 0 | 210 |
| 10 | 1003 | 210 | -50 | 160 |
| 11 | 1003 | 160 | 0 | 160 |
+------+--------+-------+----------+-----+
Demo