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 When you use UNION, you cant include any column of type TEXT and NTEXT. But it is possible if you use UNION ALL Declare @test table ( i int , text_col text ) insert into @test select 1 , 'some test...(<a href="http://sqlserver-qa.net/blogs/t-sql/archive/2008/04/03/3955.aspx">read more</a>)<img src="http://sqlserver-qa.net/aggbug.aspx?PostID=3955" width="1" height="1">