SQL Server 2008: DateDiff() of Min()/ Max() not working

Question

Could you help me out with the following query?

My goal:

For each day and for each employee select minimum datetime and the maximum datetime and get the time difference in minutes

My query :

SELECT 
   PersonalId, Name, LastName, 
   Min(TmsPrick) as MinDatetime, 
   Max(TmsPrick) as MaxDatetime, 
   DATEDIFF(mi, MIN(TmsPrick), MAX(TmsPrick)) AS Expr1
FROM 
   prickTable
GROUP BY 
   DATEPART(dy, TmsPrick), PersonalId, name, lastname, TmsPrick
ORDER BY 
   PersonalId, TmsPrick

Note: DATEPART(dy, TmsPrick) = Day of year

My expected output

  PersonalId | Name      | LastName   | MinDatetime       | MaxDatetime        | Expr1
  ------------------------------------------------------------------------------------
   000001    | A         | AC         |2014-01-05 07:12:00|2014-01-05 16:00:00 | 528
   000001    | A         | AC         |2014-01-06 07:08:00|2014-01-05 16:00:00 | 532
   000001    | A         | AC         |2014-01-07 07:11:00|2014-01-07 16:00:00 | 529
   000002    | B         | BD         |2014-01-05 07:11:00|2014-01-05 16:00:00 | 529

The output I'm getting:

  PersonalId | Name      | LastName   | MinDatetime       | MaxDatetime        | Expr1
  ------------------------------------------------------------------------------------
   000001    | A         | AC         |2014-01-05 07:12:00|2014-01-05 16:00:00 | 1053168
   000001    | A         | AC         |2014-01-06 07:08:00|2014-01-05 16:00:00 | 532
   000001    | A         | AC         |2014-01-07 07:11:00|2014-01-07 16:00:00 | 529
   000002    | B         | BD         |2014-01-05 07:11:00|2014-01-05 16:00:00 | 1053169

Any idea why my output shows such differences?

Thanks

Note: The values in Tmsprick may vary from several a day to 2 in a week. The table contains values from over 3 years.

Answer 1

I suspect that the query that you want is:

SELECT PersonalId, Name, LastName,
       Min(TmsPrick) as Mintime, Max(TmsPrick) as Maxtime, 
       DATEDIFF(mi, MIN(TmsPrick), MAX(TmsPrick)) AS Expr1
FROM prickTable
GROUP BY PersonalId, name, lastname, cast(TmsPrick as date)
ORDER BY PersonalId, max(TmsPrick);

This will give the the "elapsed" time on each day, because the first and last "tmsprick".

Answer 2

Well, without seeing the source data it's hard to know for sure, but you're using different date columns in the MAX/MIN and DATEDIFF:

SELECT 
    PersonalId, 
    Name, 
    LastName, 
    Min(TmsPrick) as MinDatetime, 
    Max(TmsPrick) as MaxDatetime , 
    DATEDIFF(mi, MIN(tijdstip), MAX(tijdstip)) AS Expr1
                     ^-- should be TmsPrick?