Cartesian time data across multiple hourly rows

Question

Looking for a solution for exploding time rows into multiple rows by hour. For example, take a row like this:
EventTime         EventLengthSeconds
2014-04-25 13:31:16.857 6657
What I need is multiple rows to allocate the time by hour like this:
EventTime         EventLengthSeconds
2014-04-25 13:31:16 1724
2014-04-25 14:00:00 3600
2014-04-25 15:00:00 1333
I've crafted a solution using a derived table that I cross join to then use case statements, etc. but it's super ugly and I'm embarrassed to post it. 
I'm thinking in SQL 2012 there must be a elegant and efficient way to do this with the new windowing functions that are available. 
Thanks for any insights and suggestions.

Answer 1

You need a table of hours for this problem. The more general concept is a table of numbers. That is, a table that spans the dimension you are working and provides a row for each discrete value.
Below is an example how you can fill the table and then a query which uses this table:
CREATE TABLE Hours (Hour smalldatetime NOT NULL PRIMARY KEY);
WITH digits (d) AS (
   SELECT 1 UNION SELECT 2 UNION SELECT 3 UNION
   SELECT 4 UNION SELECT 5 UNION SELECT 6 UNION
   SELECT 7 UNION SELECT 8 UNION SELECT 9 UNION
   SELECT 0)
INSERT Hours (Hour)
   SELECT dateadd(Hour, Number, '20000101')
   FROM   (SELECT i.d + ii.d * 10 + iii.d * 100 + iv.d * 1000 +
                  v.d * 10000 + vi.d * 100000 AS Number
           FROM   digits i
           CROSS  JOIN digits ii
           CROSS  JOIN digits iii
           CROSS  JOIN digits iv
           CROSS  JOIN digits v
           CROSS  JOIN digits vi) AS Numbers
   WHERE  Number > 0
     AND  dateadd(Hour, Number, '20000101') < '20500101'
DECLARE @eventtime datetime2(3) = '2014-04-25 13:31:16.857',
        @eventspan int          = 6657
SELECT @eventtime AS EventTime,
       3600 - (60*datepart(minute, @eventtime) +
                  datepart(second, @eventtime)) AS EventSeconds
UNION ALL
SELECT Hour,
       CASE WHEN dateadd(second, @eventspan, @eventtime) >
                 dateadd(HOUR, 1, Hour)
            THEN 3600
            ELSE datediff(SECOND, Hour, dateadd(second, @eventspan, @eventtime))
      END
FROM   Hours
WHERE  Hour > @eventtime
  AND  Hour < dateadd(SECOND, @eventspan, @eventtime)
Erland Sommarskog, SQL Server MVP, [email protected]