/*********************************
Removes any characters from 
@myString that do not meet the 
provided criteria.
*********************************/
CREATE FUNCTION dbo.GetCharacters(@myString varchar(500), @validChars varchar(100))
RETURNS varchar(500) AS
BEGIN
 
	While @myString like '%[^' + @validChars + ']%'
		Select @myString = replace(@myString,substring(@myString,patindex('%[^' + @validChars + ']%',@myString),1),'')

	Return @myString
END
Go

Declare @testStr varchar(1000),
	@i int

Set @i = 1
while @i < 255
	Select 
		@TestStr = isnull(@TestStr,'') + isnull(char(@i),''), 
		@i = @i + 1

Select @TestStr
Select dbo.GetCharacters(@TestStr,'a-z')
Select dbo.GetCharacters(@TestStr,'0-9')
Select dbo.GetCharacters(@TestStr,'0-9a-z')
Select dbo.GetCharacters(@TestStr,'02468bferlki')

While @myString like '%[^' + @validChars + ']%'
		Select @myString = replace(@myString,substring(@myString,patindex('%[^' + @validChars + ']%',@myString),1),'')

	Return @myString