Question

We have a table called Events, with columns Id(int), EventDate(DateTime), EventStart(datetime) and EventEnd(datetime).

All events start and end on a single day (i.e. no events end the next day), however events in a given date may overlap between them (including one of them could cover another entirely).

Any number of events may occur for a given date.

I would like to, for a single day calculate the total duration during which at least one event was running in T-SQL. I can select the events on a given date, and have even written a function returning true if two events are overlapping and false if not.

I am stuck however in how to take the records in pairs and run them through my function, adding the durations appropriately until I run out of events.

Can you help?

Chris

Answer 1

Try this:

--test table
declare @t table(fromt datetime, tot datetime)
--test data
insert @t values('2011-01-01 10:00', '2011-01-01 11:00')
insert @t values('2011-01-01 10:00', '2011-01-01 10:05')
insert @t values('2011-01-01 10:30', '2011-01-01 11:30')
insert @t values('2011-01-01 12:00', '2011-01-01 12:30')
insert @t values('2011-01-02 12:00', '2011-01-02 12:30')

--query
;with f as
(
    select distinct fromt from @t t 
    where not exists(select 1 from @t where t.fromt > fromt and t.fromt < tot)
), t as
(
    select distinct tot from @t t 
    where not exists(select 1 from @t where t.tot >= fromt and t.tot < tot)
), s as
(
    select datediff(day, 0, fromt) d, datediff(second, fromt, (select min(tot) 
      from t where f.fromt < tot and datediff(day, f.fromt, tot) = 0)) sec 
    from f
)
select dateadd(day, 0, d) day, sum(sec)/60 [minutes]
from s
group by d
order by d

Result:

day                     minutes
----------------------- -------
2011-01-01 00:00:00.000 120
2011-01-02 00:00:00.000 30