Find difference between rows of same column (difference between time data) - asp.net

Question

I want to find difference between time data which is in same column for group of same employee. I have written a query as below:
WITH rows AS
(
SELECT isnull(left(hhmm,2)+ ':'+ right(left(hhmm,4),2),'''') as login,
ROW_NUMBER() OVER (ORDER BY cardno) AS rn
FROM ATTN01072013_copy13_7_13
)
SELECT *--mc.login-mp.login as diff
FROM rows mc
JOIN rows mp
ON mc.rn = mp.rn - 1
This query will return data like this:
cardno login rn cardno login rn
E44920 09:18 1 E44920 09:46 2
E44920 09:46 2 E44920 17:09 3
E44920 17:09 3 E44920 16:57 4
E44920 16:57 4 E44920 17:34 5
E44920 17:34 5 E44920 17:53 6
E44920 17:53 6 E44920 17:56 7
E44920 17:56 7 E44920 17:57 8
E44920 17:57 8 E44920 18:00 9
Now I want to find difference between 1st and 2nd login time.. then 3rd and 4th login time. How can I do this, kindly suggest solution asap, thanks.

Answer 1

Solution:
DECLARE #Event TABLE(
EventID INT IDENTITY(1,1) NOT NULL PRIMARY KEY,
CardNo VARCHAR(10) NOT NULL,
[Login] DATETIME NOT NULL
-- To prevent duplicate events
-- This constraint will create an index used to optimize the RowNum and the last queries
UNIQUE(CardNo,[Login])
);
INSERT INTO #Event(CardNo,[Login])
SELECT 'E44920', '2013-07-15T09:18:00'
UNION ALL SELECT 'E44920', '2013-07-15T09:46:00'
UNION ALL SELECT 'E44920', '2013-07-15T17:09:00'
UNION ALL SELECT 'E44920', '2013-07-15T16:57:00'
UNION ALL SELECT 'E44920', '2013-07-15T17:34:00'
UNION ALL SELECT 'E44920', '2013-07-15T17:53:00';
DECLARE #EventWithRowNum TABLE(
RowNum INT NOT NULL,
CardNo VARCHAR(10) NOT NULL,
PRIMARY KEY (CardNo,RowNum),
[Login] DATETIME NOT NULL
UNIQUE(CardNo,[Login])
);
INSERT INTO #EventWithRowNum (CardNo,[Login],RowNum)
SELECT e.CardNo, e.[Login], ROW_NUMBER() OVER(PARTITION BY e.CardNo ORDER BY e.[Login]) AS RowNum
FROM #Event e;
-- Final query
SELECT crt.RowNum,
crt.CardNo,
crt.[Login] AS CurrentLogin,
nxt.RowNum,
nxt.[Login] AS NextLogin,
DATEDIFF(SECOND, crt.Login, nxt.Login) AS Diff_Seconds
FROM #EventWithRowNum crt -- crt = odd rows
LEFT JOIN #EventWithRowNum nxt ON crt.CardNo=nxt.CardNo AND crt.RowNum=nxt.RowNum-1 -- nxt = even rows
WHERE crt.RowNum % 2 = 1 -- odd rows; you could add a computed column Modulo2 AS (RowNum % 2) PERSISTED and then you could define a index (key: Modulo2, CardNo, Login)
ORDER BY crt.CardNo, crt.[Login];
Results:
RowNum CardNo Current_Login RowNum Next_Login Diff_Seconds
----------- ---------- ----------------------- ----------- ----------------------- ------------
1 E44920 2013-07-15 09:18:00.000 2 2013-07-15 09:46:00.000 1680
3 E44920 2013-07-15 16:57:00.000 4 2013-07-15 17:09:00.000 720
5 E44920 2013-07-15 17:34:00.000 6 2013-07-15 17:53:00.000 1140

Answer 2

Try:
DATEDIFF (mi, CAST(mc.login AS DATETIME), CAST(mp.login AS DATETIME)) as diff
This will get difference in minutes
SQLFiddle DEMO

Answer 3

Here is a fully query you can try using. As Nenad Zivkovic already shown, idea is to use DATEDIFF function for this.
Only difference is that I’d suggest using full date time for calculating the difference to avoid possible issues when one login is like 22:03 and other one is 00:16.
WITH rows AS
(
SELECT isnull(left(hhmm,2)+ ':'+ right(left(hhmm,4),2),'''') as login,
hhmm as Full_Login,
ROW_NUMBER() OVER (ORDER BY cardno) AS rn
FROM ATTN01072013_copy13_7_13
)
SELECT mc.login,
mc.rn,
DATEDIFF(mi,mc.Full_Login, mp.Full_Login)
mp.login,
mc.rn
FROM rows mc
JOIN rows mp
ON mc.rn = mp.rn