Question

I have these fields in my T-SQL database – startTime and endTime and processTime.
The process time is the amount of time from start to end time.
So, one startTime example is 22:50:59 and its endTime is 23:14:23.
Process time would be .39 (The current code):

SELECT convert( decimal(18,0), totalItems 
        /(datediff(ss,sessionStartTime,sessionEndTime)/60.00/60.00) ) 
  AS processTime

This seems to be working for the most part, but it doesn’t work when the startTime and endTime span across a day – for example, a startTime is 23:17:27 and an endTime of 00:31:23.

In other words, they started at 10:17 p.m., and finished at about 12:31 a.m. the following morning, but SQL isn’t seeing this, because the processTime is displaying as a negative number (-22.77)…
How do I convert these negative times into positive times?

I do have separate date fields – a startDate, and an endDate.

Answer 1

I’m assuming you’re including dates…(?)

Here is a sample I ran — seems to work as expected:

declare @start datetime
declare @end datetime

set @start = '2011-09-06 23:17:27'
set @end = '2011-09-07 00:31:23'

select 
    datediff(second,@start,@end) as seconds, 
    datediff(minute,@start,@end) as minutes,
    datediff(hour,@start,@end) as hours,
    datediff(day,@start,@end) as days,
    datediff(month,@start,@end) as months,
    datediff(year,@start,@end) as years

Here’s the results:

seconds     minutes     hours       days        months      years
----------- ----------- ----------- ----------- ----------- -----------
4436        74          1           1           0           0

(1 row(s) affected)

One thing you might do is re-check the scope of your decimal conversion. E.g.: this produces a different results, depending on where you put the parens before the division:

declare @start datetime
declare @end datetime

set @start = '2011-09-06 23:17:27'
set @end = '2011-09-07 00:31:23'

select convert(decimal(18,0), (datediff(ss,@start,@end)))/60.00/60.00 as NEW_processTime,
       convert(decimal(18,0), (datediff(ss,@start,@end)/60.00/60.00)) as ORIGINAL_processTime

Here are the results of that:

NEW_processTime                         ORIGINAL_processTime
--------------------------------------- ---------------------------------------
1.23222221666                           1

(1 row(s) affected)