How to sum the activity time that occurred within 15-minute intervals using overlapping start and stop times(SQL)(t-SQL)

Question

I\'d like to write a query that will calculate the total amount of activity that occurred within each 15 minute interval of the day using only timestamps that correspond to acti

Answer 1

Assuming some reasonable recent version of SQL Server, this ought to be a good start:

-- Some sample data.
declare @Samples as Table ( SampleId Int Identity, Start DateTime, Stop DateTime );
insert into @Samples ( Start, Stop ) values
  ( '2/2/2015 7:00', '2/2/2015 7:25' ),
  ( '2/2/2015 7:20', '2/2/2015 7:29' ),
  ( '2/2/2015 7:35', '2/2/2015 7:42' ),
  ( '2/2/2015 8:05', '2/2/2015 8:14' ),
  ( '2/2/2015 8:16', '2/2/2015 8:20' ),
  ( '2/2/2015 8:29', '2/2/2015 8:40' ),
  ( '2/2/2015 8:55', '2/2/2015 9:25' );
select * from @Samples;

-- Find the limits and align them to quarter hours.
declare @Min as DateTime;
declare @Max as DateTime;
select @Min = min( Start ), @Max = max( Stop )
  from @Samples;
set @Min = DateAdd( minute, -DatePart( minute, @Min ) % 15, @Min );
set @Max = DateAdd( minute, 15 - DatePart( minute, @Max ) % 15, @Max );
select @Min as [Min], @Max as [Max];


-- Go for it.
with QuarterHours ( QuarterStart, QuarterStop )
  as (
    select @Min, DateAdd( minute, 15, @Min )
    union all
    select QuarterStop, DateAdd( minute, 15, QuarterStop )
      from QuarterHours
      where QuarterStop < @Max ),
  Overlaps
  as ( select QH.QuarterStart, QH.QuarterStop, S.Start, S.Stop,
  case
    when S.Start <= QH.QuarterStart and S.Stop >= QH.QuarterStop then 15
    when S.Start <= QH.QuarterStart and S.Stop < QH.QuarterStop then DateDiff( minute, QH.QuarterStart, S.Stop )
    when S.Start > QH.QuarterStart and S.Stop >= QH.QuarterStop then DateDiff( minute, S.Start, QH.QuarterStop )
    when S.Start > QH.QuarterStart and S.Stop < QH.QuarterStop then DateDiff( minute, S.Start, S.Stop )
    else 0 end as Overlap
  from QuarterHours as QH left outer join
    @Samples as S on S.Start <= QH.QuarterStop and S.Stop >= QH.QuarterStart )
  select QuarterStart, sum( Overlap ) as [ActivityTime]
    from Overlaps
    group by QuarterStart
    order by QuarterStart;

You can change the last select to either select * from QuarterHours or select * from Overlaps to see some of the intermediate values.

Explanatory notes:

You can use any range (@Min/@Max) you want, I just took them from the sample data so that the example would run. I used a table variable for the same reason, no need to create a "real" table for the sake of an example.

The Common Table Expression (CTE) creates, via recursion, a table of QuarterHours that covers the desired range. (A numbers table or tally table could also be used to generate the quarter hours.) Then a LEFT OUTER JOIN with the sample data is used to locate all of the Overlaps, if any, with each quarter hour. That preserves the quarter hours for which there is no activity.

The final SELECT summarizes the results.