Fortunately for you SQL 2012 has much better Windowing Function support. Look into the PERCENTILE_CONT function. I also HIGHLY recommend you purchase Itzik Ben-Gan's SQL Server 2012 High-Performance TSQL Using Window Functions book.
Just an interesting FYI...
I have never used PERCENTILE_CONT but I do have Server 2012 High-Performance TSQL Using Window Functions. With the same sample data from earlier (#T), this is a modified version of Ben-Gan's 2012-based solution using PERCENTILE_COUNT:
WITH t(r,m) AS
( SELECT ROW_NUMBER() OVER(ORDER BY (SELECT NULL)),
PERCENTILE_CONT(0.5) WITHIN GROUP(ORDER BY i) OVER(PARTITION BY NULL)
SELECT m AS median
Though it is much simpler, Ben-Gan's 2012-PERCENTILE_CONT solution is about twice as slow as any other solution posted thus far. Again, just an FYI.
Yep, but the book covers other non-2012 solutions for median as well (and has lots of other great stuff in it) so it was definitely worth the recommendation.
I will add that it is quite amazing how varied solutions to the same problem can be achieved in TSQL, and just as amazing how varied the performance characteristics of those solutions can be!!
Kevin G. Boles
SQL Server Consultant
SQL MVP 2007-2012
TheSQLGuru at GMail