Question

I have a table with column StartDate, I want to calculate the time difference between two consecutive record.

Thanks.

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@ Mark Byers and @ Yahia, I have request table as requestId, startdate

requestId    startdate               
1            2011-10-16 13:15:56
2            2011-10-16 13:15:59
3            2011-10-16 13:15:59
4            2011-10-16 13:16:02
5            2011-10-16 13:18:07

and i want to know what is the time difference between requestid 1 & 2, 2 & 3, 3 & 4 and so on. i know i will need self join on table, but i am not getting correct on clause.

Answer 1

To achieve what you are asking try the following (UPDATE after edit from OP):

SELECT A.requestid, A.starttime, (B.starttime - A.starttime) AS timedifference
FROM MyTable A INNER JOIN MyTable B ON B.requestid = (A.requestid + 1)
ORDER BY A.requestid ASC

IF requestid is not consecutive then you can use

SELECT A.requestid, A.starttime, (B.starttime - A.starttime) AS timedifference
FROM MyTable A CROSS JOIN MyTable B
WHERE B.requestid IN (SELECT MIN (C.requestid) FROM MyTable C WHERE C.requestid > A.requestid)
ORDER BY A.requestid ASC