sql server: peak active users by date range - sql

Question

I needs to get count of max active users by date range.
Acrive users - it is a maximum number of not removed users.
I have UsersHistory Table:
HistoryID UserID IsRemoved OperationID ModificationDate
----------------------------------------------------------------------
1 1 0 'Add' 2012-07-24 04:27:48
2 2 0 'Add' 2012-07-26 04:18:48
3 3 0 'Add' 2012-07-27 04:29:48
4 1 0 'Update' 2012-07-28 04:47:48
5 2 0 'Update' 2012-07-29 04:01:48
6 1 1 'Remove' 2012-08-28 04:34:48
7 2 1 'Remove' 2012-08-28 04:18:48
8 3 1 'Remove' 2012-08-28 04:29:48
9 4 0 'Add' 2012-09-24 04:27:48
10 5 0 'Add' 2012-09-26 04:18:48
11 6 0 'Add' 2012-09-27 04:29:48
12 7 0 'Add' 2012-09-27 04:29:48
Expected result: Max active users by this period: 4 (HistoryID: 9, 10, 11, 12)
Update1:
HistoryID UserID IsRemoved OperationID ModificationDate
----------------------------------------------------------------------
1 1 0 'Add' 2012-07-24 04:27:48
2 2 0 'Add' 2012-07-26 04:18:48
3 3 0 'Add' 2012-07-27 04:29:48
4 1 1 'Remove' 2012-07-28 04:47:48
5 2 1 'Remove' 2012-07-28 04:47:48
6 3 1 'Remove' 2012-07-28 04:47:48
Expected result: Maximum of active(not removed) users by this period: 3

Answer 1

This should work for you. It will count total number of operations Add and total operations of Remove. After It subract total count of Remove from total count of Add.
DECLARE #counter1 INT,
#counter2 INT,
#result INT
SELECT #counter1 = c1
FROM(
SELECT COUNT(HistoryID) AS c1
FROM UsersHistory
WHERE OperationId = 'Add'
) x
SELECT #counter2 = c2
FROM(
SELECT COUNT(HistoryID) AS c2
FROM UsersHistory
WHERE OperationId = 'Remove'
) a
SET #result = #counter1 - #counter2
SELECT #result
EDIT
Here you go (It should count maximum as you need):
SELECT TOP 1 COUNT(*) AS maxRes
FROM (
SELECT DENSE_RANK() OVER (ORDER BY UserID ASC) AS [MaximumCount], *
FROM UsersHistory
WHERE OperationId = 'Add'
) a
WHERE
[MaximumCount] = UserID
GROUP BY MaximumCount
ORDER BY maxRes DESC

Answer 2

If I understand you correctly you need to make islands by OperationID and count maximum count of rows in 'Add' islands. If so then:
DECLARE #History TABLE
(
HistoryID INT ,
UserID INT ,
IsRemoved BIT ,
OperationID NVARCHAR(20)
)
INSERT INTO #History
VALUES ( 1, 1, 0, 'Add' ),
( 2, 2, 0, 'Add' ),
( 3, 3, 0, 'Add' ),
( 4, 1, 1, 'Remove' ),
( 5, 2, 1, 'Remove' ),
( 6, 3, 1, 'Remove' ),
( 7, 3, 0, 'Add' );
WITH cte1
AS ( SELECT OperationID ,
ROW_NUMBER() OVER ( ORDER BY HistoryID ) AS ID ,
1 AS Dummy ,
IIF(ISNULL(LAG(OperationID) OVER ( ORDER BY HistoryID ),
OperationID) = OperationID, 0, 1) AS ChangeMark
FROM #History
),
cte2
AS ( SELECT * ,
SUM(Dummy) OVER ( ORDER BY ID )
+ SUM(ChangeMark) OVER ( ORDER BY ID ) AS InervalID
FROM cte1
),
cte3
AS ( SELECT StartSeqNo = MIN(InervalID) ,
EndSeqNo = MAX(InervalID)
FROM ( SELECT InervalID ,
rn = InervalID
- ROW_NUMBER() OVER ( ORDER BY InervalID )
FROM cte2
) a
GROUP BY rn
),
cte4
AS ( SELECT COUNT(*) AS C
FROM cte2 c2
JOIN cte3 c3 ON c2.InervalID BETWEEN c3.StartSeqNo AND c3.EndSeqNo
WHERE c2.OperationID = 'Add'
GROUP BY c3.EndSeqNo
)
SELECT MAX(c) AS UserCount
FROM cte4