How to remove special characters from a string in MS SQL Server (T-SQL)

-- Removes special characters from a string value.
-- All characters except 0-9, a-z and A-Z are removed and
-- the remaining characters are returned.
-- Author: Christian d'Heureuse, www.source-code.biz

create function dbo.RemoveSpecialChars (@s varchar(256))
returns varchar(256) with schemabinding
    begin 
     if @s is null 
        return null
     declare @s2 varchar(256)
     set @s2 = ''
     declare @l int
     set @l = len(@s)
     declare @p int 
     set @p = 1
     while @p <= @l
         begin
           declare @c int
           set @c = ascii(substring(@s, @p, 1))  
           if @c between 48 and 57 or
              @c between 65 and 90 or
              @c between 97 and 122    
           set @s2 = @s2 + char(@c)
           set @p = @p + 1
     end
     if len(@s2) = 0
     return null
return @s2
end

Example of how to use the function:
select dbo.RemoveSpecialChars('abc-123+ABC')
Result:
abc123ABC