Average difference between two dates, grouped by a third field?

sql

You don't specify the granularity you want for the diff. This does it in days:

select username, avg(end_date - start_date) as avg_daysfrom mytablegroup by username

If you want the difference in seconds, use datediff():

select username, avg(datediff(ss, start_date, end_date)) as avg_seconds...

datediff can measure the diff in any time unit up to years by varying the first parameter, which can be ss, mi, hh, dd, wk, mm or yy.

sql

SELECT [username], AVG(TIMESTAMPDIFF(HOUR, start_date, end_date))FROM [table]GROUP BY [username]

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