Decode URL using SQL Server

Create FUNCTION [dbo].[UrlDecode](@url varchar(max))
RETURNS varchar(MAX)
AS
BEGIN
    DECLARE @count int, @c char(1), @cenc char(2), @i int, @urlReturn varchar(MAX)
    SET @count = Len(@url)
    SET @i = 1
    SET @urlReturn = ''
    WHILE (@i <= @count)
     BEGIN
        SET @c = substring(@url, @i, 1)
        IF @c LIKE '[!%]' ESCAPE '!'
         BEGIN
            SET @cenc = substring(@url, @i + 1, 2)
            SET @c = CHAR(CASE WHEN SUBSTRING(@cenc, 1, 1) LIKE '[0-9]'
                                THEN CAST(SUBSTRING(@cenc, 1, 1) as int)
                                ELSE CAST(ASCII(UPPER(SUBSTRING(@cenc, 1, 1)))-55 as int)
                            END * 16 +
                            CASE WHEN SUBSTRING(@cenc, 2, 1) LIKE '[0-9]'
                                THEN CAST(SUBSTRING(@cenc, 2, 1) as int)
                                ELSE CAST(ASCII(UPPER(SUBSTRING(@cenc, 2, 1)))-55 as int)
                            END)
            SET @urlReturn = @urlReturn + @c
            SET @i = @i + 2
         END
        ELSE
         BEGIN
            SET @urlReturn = @urlReturn + @c
         END
        SET @i = @i +1
     END
    RETURN @urlReturn
END