Flattening intersecting timespans

Question

I have lots of data with start and stop times for a given ID and I need to flatten all intersecting and adjacent timespans into one combined timespan. The sample data posted

Answer 1

Here is a SQL only solution. I used DATETIME for the columns. Storing the time separate is a mistake in my opinion, as you will have problems when the times go past midnight. You can adjust this to handle that situation though if you need to. The solution also assumes that the start and end times are NOT NULL. Again, you can adjust as needed if that's not the case.

The general gist of the solution is to get all of the start times that don't overlap with any other spans, get all of the end times that don't overlap with any spans, then match the two together.

The results match your expected results except in one case, which checking by hand looks like you have a mistake in your expected output. On the 6th there should be a span that ends at 2009-06-06 10:18:45.000.

SELECT
     ST.start_time,
     ET.end_time
FROM
(
     SELECT
          T1.start_time
     FROM
          dbo.Test_Time_Spans T1
     LEFT OUTER JOIN dbo.Test_Time_Spans T2 ON
          T2.start_time < T1.start_time AND
          T2.end_time >= T1.start_time
     WHERE
          T2.start_time IS NULL
) AS ST
INNER JOIN
(
     SELECT
          T3.end_time
     FROM
          dbo.Test_Time_Spans T3
     LEFT OUTER JOIN dbo.Test_Time_Spans T4 ON
          T4.end_time > T3.end_time AND
          T4.start_time <= T3.end_time
     WHERE
          T4.start_time IS NULL
) AS ET ON
     ET.end_time > ST.start_time
LEFT OUTER JOIN
(
     SELECT
          T5.end_time
     FROM
          dbo.Test_Time_Spans T5
     LEFT OUTER JOIN dbo.Test_Time_Spans T6 ON
          T6.end_time > T5.end_time AND
          T6.start_time <= T5.end_time
     WHERE
          T6.start_time IS NULL
) AS ET2 ON
     ET2.end_time > ST.start_time AND
     ET2.end_time < ET.end_time
WHERE
     ET2.end_time IS NULL