Thanks, Mark,

DATEDIFF is the tough one for most folks because they frequently don't understand that it works on the BOUNDARIES of the datepart. For example, a DATEDIFF(yy,'2014-12-31 23:59:59.997','2015-01-01 00:00:00.000') will return a "1" even though the two dates are only 3ms apart.

As for CROSS APPLY, it's the same as a correlated subquery in the SELECT list except that it can return more than one value for each row without blowing up. Paul White wrote really good articles on the subject. Here are the links to those articles...

http://www.sqlservercentral.com/articles/APPLY/69953/

http://www.sqlservercentral.com/articles/APPLY/69954/