SQL Server running total with dbmail when total met or exceeded - sql-server

Question

I am able to get a running total via script--but what I can't seem to do is isolate the line where I have met or exceeded a certain value...
SELECT
column1,
(SELECT SUM(column1) FROM table WHERE column2 <= t1.column2)
FROM
table t1
Ultimately what I would want to do is create a trigger to send dbmail when the Sum of column1 meets or exceeds (n)...help me obi-wan

Answer 1

On SQL-Server 2008 you can use next solution:
DECLARE #TBL TABLE(id int, amount int);
INSERT INTO #TBL VALUES
(1, 100), (2, 100), (3, 60), (4, 200), (5, 100);
SELECT t1.ID, t1.amount, SUM(t2.amount) as CumTotal
FROM #TBL t1
CROSS APPLY (SELECT *
FROM #TBL
WHERE ID <= t1.id) t2
GROUP BY t1.ID, t1.amount
HAVING SUM(t1.amount) < 300
ORDER BY t1.ID
;
This is the result:
ID | amount | CumTotal
-: | -----: | -------:
1 | 100 | 100
2 | 100 | 200
3 | 60 | 260
dbfiddle here
Although this solution works well, it is not recommendable on terms of performance.
In this case the best option is to use a CURSOR.
DECLARE #CS table (id int, amount int, total int);
DECLARE #id int, #amount int;
DECLARE #CumSum int = 0;
DECLARE c CURSOR
LOCAL STATIC FORWARD_ONLY READ_ONLY
FOR SELECT ID, amount
FROM #TBL
ORDER BY [id];
OPEN c;
FETCH NEXT FROM c INTO #id, #amount
WHILE ##FETCH_STATUS = 0 AND #CumSum + #amount < 300
BEGIN
SET #CumSum = #CumSum + #amount;
INSERT #CS (id, amount, total)
SELECT #id, #amount, #CumSum;
FETCH NEXT FROM c INTO #id, #amount
END
CLOSE c;
DEALLOCATE c;
SELECT id, amount, total
FROM #CS
ORDER BY id;
GO
id | amount | total
-: | -----: | ----:
1 | 100 | 100
2 | 100 | 200
3 | 60 | 260
dbfiddle here
Next answer can be used on SQL-SERVER 2012 and above
You can use a cumulative sum using a WINDOW function and SUM() ROWS UNBOUNDED PRECEDING.
Have a look at MS docs.
DECLARE #TBL TABLE(id int, amount int);
INSERT INTO #TBL VALUES
(1, 100), (2, 100), (3, 60), (4, 200), (5, 100);
Next query returns a cumulative sum:
SELECT ID,
SUM(amount) OVER (ORDER BY ID ROWS UNBOUNDED PRECEDING) AS CumTotal
FROM #TBL
;
ID | CumTotal
-: | -------:
1 | 100
2 | 200
3 | 260
4 | 460
5 | 560
The problem is that you cannot stop it, you need to calculate all records, and then you can apply a where clause just to filter the records.
WITH CSum As
(
SELECT ID,
SUM(amount) OVER (ORDER BY ID ROWS UNBOUNDED PRECEDING) AS CumTotal
FROM #TBL
)
SELECT ID, CumTotal
FROM CSum
WHERE CumTotal < 300
ORDER BY ID
;
This is the final result:
ID | CumTotal
-: | -------:
1 | 100
2 | 200
3 | 260
dbfiddle here