Combine rows when the end time of one is the start time of another

Question

I am having difficulty writing a query. I need to combine rows of time-consecutive states into a single state. For example, given the data:

start                    end                      state   seconds
2011-04-21 08:13:30.000  2011-04-21 08:18:00.000  STATE1  270
2011-04-21 08:18:00.000  2011-04-21 08:22:30.000  STATE1  270
2011-04-21 08:22:30.000  2011-04-21 08:26:26.000  STATE1  236
2011-04-21 08:26:26.000  2011-04-21 08:26:47.000  STATE2  21
2011-04-21 08:26:47.000  2011-04-21 08:27:30.000  STATE3  43
2011-04-21 08:27:30.000  2011-04-21 08:28:20.000  STATE1  50
2011-04-21 08:40:30.000  2011-04-21 08:41:00.000  STATE1  30

I need to combine rows only when row2.state = row1.state AND row2.start = row1.end and come up with an overall start and end time of the state. The result should be:

start                    end                      state   seconds
2011-04-21 08:13:30.000  2011-04-21 08:26:26.000  STATE1  776
2011-04-21 08:26:26.000  2011-04-21 08:26:47.000  STATE2  21
2011-04-21 08:26:47.000  2011-04-21 08:27:30.000  STATE3  43
2011-04-21 08:27:30.000  2011-04-21 08:28:20.000  STATE1  50
2011-04-21 08:40:30.000  2011-04-21 08:41:00.000  STATE1  30

Here is the example SQL:

CREATE TABLE Data (
    ID int IDENTITY(1,1) not null,
    Date DateTime not null,
    State nvarchar(40) not null,
    Seconds int not null,
    PRIMARY KEY(ID)
);
INSERT INTO Data(Date,State,Seconds) VALUES('2011-04-21 08:13:30.000', 'STATE1', 270)
INSERT INTO Data(Date,State,Seconds) VALUES('2011-04-21 08:18:00.000', 'STATE1', 270)
INSERT INTO Data(Date,State,Seconds) VALUES('2011-04-21 08:22:30.000', 'STATE1', 236)
INSERT INTO Data(Date,State,Seconds) VALUES('2011-04-21 08:26:26.000', 'STATE2', 21)
INSERT INTO Data(Date,State,Seconds) VALUES('2011-04-21 08:26:47.000', 'STATE3', 43)
INSERT INTO Data(Date,State,Seconds) VALUES('2011-04-21 08:27:30.000', 'STATE1', 50)
INSERT INTO Data(Date,State,Seconds) VALUES('2011-04-21 08:40:30.000', 'STATE1', 30)

SELECT Date as 'start', DATEADD(s,Seconds,Date) as 'end', State, Seconds FROM Data

Thanks in advance!

Answer 1

Try this(>= SQL Server 2005):

WITH qry AS
(
    SELECT  a.*
                    ,ROW_NUMBER() OVER (ORDER BY [start]) rn
    FROM    (SELECT Date as 'start', DATEADD(s,Seconds,Date) as 'end', State, Seconds FROM Data) a
)
SELECT  DISTINCT MIN(a.start) OVER(PARTITION BY a.State, a.[end] - ISNULL(b.start, a.start)) ,
                MAX(a.[end] ) OVER(PARTITION BY a.State, a.[end] - ISNULL(b.start, a.start)) ,
                a.state
                ,SUM(a.Seconds) OVER(PARTITION BY a.State, a.[end] - ISNULL(b.start, a.start)) 

  FROM qry a LEFT JOIN qry b
        ON a.rn + 1 = b.rn
   AND a.[end] = b.start