Madhivanan

Union Vs Union All

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 string'union all
select 2,'some other test string'
 
--Error
select i,text_col from @test where i=1union 
select i,text_col from @test where i=1
--No Error
 select i,text_col from @test where i=1union all
select i,text_col from @test where i=1