I agree with a column type of char(10) as you say. When it is nvarchar(250) on SQL Serveur 2005 if you run the following query :

SELECT LEN(fieldname) FROM table;

you will...

Yes, but this is not the problem.

The exact problem is that for SQL norm if you compare two string with different lengths the first thing done by SQL is to...

I found the reason why 'a' is equal to 'a ' or 'a '.

ANSI Standard : Have a look to :

http://msdn.microsoft.com/en-us/library/ms187403.aspx