Remove duplicate characters from a string

Pinal Dave in his weblog posted about Remove Duplicate Chars From String

Here is its alternate method with Number table approach

create procedure remove_duplicate_characters(@string varchar(100))
as
Declare @result varchar(100)

set @result=''

select @result=@result+min(substring(@string ,number,1)) from 
( 
    select number from master..spt_values where type='p' and number between 1 and len(@string )
) as t 
group by substring(@string,number,1)
order by min(number)

select @result 
GO

EXEC remove_duplicate_characters 'aasssarrrty'
 
returns
 
asrty