How to merge time intervals in SQL Server

Question

Suppose I have the following an event table with personId, startDate and endDate.

I want to know how much time the person X sp

Answer 1

Algebra. If B-n is the ending time of the nth event, and A-n is the starting time of the nth event, then the sum of the differences is the difference of the sums. So you can write

select everything else, sum(cast(endDate as int)) - sum(cast(startDate as int)) as daysSpent

If your dates have no time component, this works. Otherwise, you could use a real.