Get list with start and end values from table of datetimes

Question

Currently i have a table built up like this way

DeviceID      Timestamp            Value
----------------------------------------
Device1       1.1.2011 10:0         


        

Answer 1

I've played around with some datatypes and names (just because I can, and because timestamp is a reserved word), and can get your requested result using your sample data.

Sample data:

create table Measures (
    DeviceID int not null,
    Occurred datetime not null,
    Value int not null,
    constraint PK_Measures PRIMARY KEY (DeviceID,Occurred)
)
go
insert into Measures (DeviceID,Occurred,Value)
select 1,'2011-01-01T10:00:00',3 union all
select 1,'2011-01-01T10:00:01',4 union all
select 1,'2011-01-01T10:00:02',4 union all
select 1,'2011-01-01T10:00:04',3 union all
select 1,'2011-01-01T10:00:05',4 union all
select 1,'2011-01-01T14:23:14',8 union all
select 1,'2011-01-01T14:23:15',7 union all
select 1,'2011-01-01T14:23:17',4 union all
select 1,'2011-01-01T14:23:18',2

and now the query:

;with StartPeriods as (
    select m1.DeviceID,m1.Occurred as Started
    from Measures m1 left join Measures m2 on m1.DeviceID = m2.DeviceID and m2.Occurred < m1.Occurred and DATEDIFF(second,m2.Occurred,m1.Occurred) < 6
    where m2.DeviceID is null
), ExtendPeriods as (
    select DeviceID,Started,Started as Ended from StartPeriods
    union all
    select
        ep.DeviceID,ep.Started,m2.Occurred
    from
        ExtendPeriods ep
            inner join
        Measures m2
            on
                ep.DeviceID = m2.DeviceID and
                ep.Ended < m2.Occurred and
                DATEDIFF(SECOND,ep.Ended,m2.Occurred) < 6
)
select DeviceID,Started,MAX(Ended) from ExtendPeriods group by DeviceID,Started

The StartPeriods Common Table Expression (CTE) finds those rows from the Measures table that don't have a previous row within 5 seconds of them. The ExtendPeriods CTE then recursively extends these periods by finding new rows from Measures that occur up to 5 seconds after the current end of the found period.

We then find the rows where the end of the period was as far away from the start as possible.