DATEDIFF in HH:MM:SS format

Question

I need to calculate the total length in terms of Hours, Minutes, Seconds, and the average length, given some data with start time and end time.

For example the resul

Answer 1

A way that avoids overflows and can include days and go all the way to milliseconds in the output:

DECLARE @startDate AS DATETIME = '2018-06-01 14:20:02.100'
DECLARE @endDate AS DATETIME = '2018-06-02 15:23:09.000'
SELECT CAST(DATEDIFF(day,'1900-01-01', @endDate - @startDate) AS VARCHAR) +  'd ' + CONVERT(varchar(22), @endDate - @startDate, 114)

The above will return

1d 01:03:06:900

And, off course, you can use the formatting of your choice

SQL Supports datetime substraction which outputs a new datetime relative to the MIN date (for instance 1900-01-01, you can probably get this value from some system variable) This works better than DATEDIFF, because DATEDIFF will count ONE for each "datepart boundaries crossed", even if the elapsed time is less than a whole datapart. Another nice thing about this method is that it allows you to use the date formatting conversions.