Calculating The Time Duration For Each Event

Hi all,

Thanks for setting up such a great site and forum.

Here is my problem:

I have a table like the following in SQL Server 2005:


order | taskid | main_person | temp_person | start_assign_date
1 | 3 | John | John | 2008-01-01 10:20:22
2 | 3 | John | Joe | 2008-02-05 15:20:22
3 | 3 | John | John | 2008-02-07 20:25:20
4 | 6 | Joe | Joe | 2008-01-01 10:20:22
5 | 6 | Joe | Mike | 2008-02-01 10:20:22
6 | 10 | Doug | Doug | 2008-01-01 10:20:22
7 | 7 | Russ | Russ | 2008-02-01 11:20:22
8 | 7 | Russ | Mike | 2008-02-08 12:20:22
9 | 7 | Russ | John | 2008-02-10 20:05:12


It was made to record who was in charge of a specific task at a specific time. Each task has its own main responsible person and some substitutes for that person as Temporary Persons (who did the task while main person was away). The Main Person's name is in the temp_person column when he is doing the task by himself.

I'd like to generate a report that shows:
- in a specific time period
- which persons were in charge of a specific task and
- for how long

Something like this:

From 2008-##-## to 2008-##-##
Task 3 - John - 15 days
Task 3 - Joe - 5 days
Task 6 - Joe - 18 days
Task 6 - Mike - 2 days
Task 10 - Doug - 20 days


I have some ideas to do that when there are both start and end dates for every record but I couldn't find a way to use the next assignment start date for each task, as the end date for its previous record (in that task group) to calculate the duration for that record.

I can group the tasks and users and put them in the chronological order but I can't indicate the next start date as the end date for the previous record (in specific task group) to use the date difference functions.

Any hint or comment would be appreciated.

Thanks
Sami