How to Calculate Time Difference Between Consecutive Rows in a SQL Table?

Calculating Time Difference Between Consecutive Rows

The task is to determine the time difference between consecutive records in a table containing a StartDate column. To achieve this, we can utilize a self-join and compare each record with its subsequent record in the table.

Using a Self-Join:

To compare consecutive records, we can use a self-join on the table. Here's an example query:

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;

This query creates a joined table where each record (A) is paired with its next record (B). The computed column timedifference gives the time difference between the two records.

Handling Non-Consecutive Request Ids:

If the request ids are not consecutive, we can use a CROSS JOIN and additional filtering to match each record with its immediate successor.

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;

This query ensures that each record is matched with its immediate successor, even if the request ids are not consecutive.

Sample Data:

Consider the sample data provided by the author:

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

Output:

Applying the above query to the sample data will produce the following output:

requestId	startdate	timedifference
1	2011-10-16 13:15:56	NULL
2	2011-10-16 13:15:59	00:00:03
3	2011-10-16 13:15:59	00:00:00
4	2011-10-16 13:16:02	00:00:03
5	2011-10-16 13:18:07	00:02:05

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