Well. Most of you know the diffrence between the two. http://blog.sqlauthority.com/2007/03/10/sql-server-union-vs-union-all-which-is-better-for-performance/ http://www.codethinked.com/post/2007/11/UNION-versus-UNION-ALL2c-lessons-in-minutiae.aspx Here is one of the differences that is not known by newbies...