Is there anyway to do this?

I have a table 
              Table "Users" Column   |          Type          | Modifiers 
-----------+------------------------+-----------userid    | character varying(40)  | not nullusername  | character
varying(64) | 
 

I want to get all the distinct first character of all usernames. And do
it in a way that is the most portable to MS SQL server.

Is there anyway?

Thanks

-- 
Wei Weng
Network Software Engineer
KenCast Inc.