Understanding existing logic in your query
UPDATE
statement will fire a trigger
only once for a set or batch satisfying join conditions, Inserted statement will have all the records that are being updated. This is because of BATCH processing not because of CROSS APPLY
but because of UPDATE
.
In this query of yours
SELECT CORP, CURRENT_TIMESTAMP, COST,
((SELECT TOP 1 BAL FROM FINS WHERE COMPANY = CORP ORDER BY TS DESC)- COST)
FROM inserted WHERE COALESCE(COST,0) <> 0
For each CORP from an Outer query, same BAL will be returned.
(SELECT TOP 1 BAL FROM FINS WHERE COMPANY = CORP ORDER BY TS DESC)
That being said, your inner query will be replaced by 1000(value you used in your example) every time CORP = 'XYZ'
SELECT CORP, CURRENT_TIMESTAMP, COST, (1000- COST)
FROM inserted WHERE COALESCE(COST,0) <> 0
Now your inserted statement has all the records that are being inserted. So every record's cost will be subtracted by 1000. Hence you are getting unexpected result.
Suggested solution
As per my understanding, you want to calculate some cumulative frequency kind of thing. Or last running total
Data Preparation for problem statement. Used my dummy data to give you an idea.
--Sort data based on timestamp in desc order
SELECT PK_LoginId AS Bal, FK_RoleId AS Cost, AddedDate AS TS
, ROW_NUMBER() OVER (ORDER BY AddedDate DESC) AS Rno
INTO ##tmp
FROM dbo.M_Login WHERE AddedDate IS NOT NULL
--Check how data looks
SELECT Bal, Cost, Rno, TS FROM ##tmp
--Considering ##tmp as your inserted table,
--I just added Row_Number to apply Top 1 Order by desc logic
+-----+------+-----+-------------------------+
| Bal | Cost | Rno | TS |
+-----+------+-----+-------------------------+
| 172 | 10 | 1 | 2012-12-05 08:16:28.767 |
| 171 | 10 | 2 | 2012-12-04 14:36:36.483 |
| 169 | 12 | 3 | 2012-12-04 14:34:36.173 |
| 168 | 12 | 4 | 2012-12-04 14:33:37.127 |
| 167 | 10 | 5 | 2012-12-04 14:31:21.593 |
| 166 | 15 | 6 | 2012-12-04 14:30:36.360 |
+-----+------+-----+-------------------------+
Alternative logic for subtracting cost from last running balance.
--Start a recursive query to subtract balance based on cost
;WITH cte(Bal, Cost, Rno)
AS
(
SELECT t.Bal, 0, t.Rno FROM ##tmp t WHERE t.Rno = 1
UNION ALL
SELECT c.Bal - t.Cost, t.Cost, t.Rno FROM ##tmp t
INNER JOIN cte c ON t.RNo - 1 = c.Rno
)
SELECT * INTO ##Fin FROM cte;
SELECT * FROM ##Fin
Output
+-----+------+-----+
| Bal | Cost | Rno |
+-----+------+-----+
| 172 | 0 | 1 |
| 162 | 10 | 2 |
| 150 | 12 | 3 |
| 138 | 12 | 4 |
| 128 | 10 | 5 |
| 113 | 15 | 6 |
+-----+------+-----+
You have to tweet your columns little bit to get this functionality into your trigger.