过滤非法字符

/// <summary>
        /// 过滤非法字符
        /// </summary>
        /// <param name="inputString1">等待处理的字符串</param>
        /// <returns></returns>
        public static string ClearRequest(object inputString1)
        {
            if (inputString1 == null) return "";
            string inputString = inputString1.ToString();
            StringBuilder retVal = new StringBuilder();
            if (inputString != String.Empty)
            {
                inputString = inputString.Trim();
                for (int i = 0; i < inputString.Length; i++)
                {
                    switch (inputString[i])
                    {
                        case '"':
                            retVal.Append("");
                            break;
                        case '<':
                            retVal.Append("");
                            break;
                        case '>':
                            retVal.Append("");
                            break;

                        default:
                            retVal.Append(inputString[i]);
                            break;
                    }
                }
                retVal = retVal.Replace("'", "");
                retVal = retVal.Replace("/", "");
                retVal = retVal.Replace("#", "");
                 retVal = retVal.Replace(".", "");
                retVal = retVal.Replace("*", "");
                retVal = retVal.Replace("+", "");
                retVal = retVal.Replace("-", "");
                retVal = retVal.Replace("$", "");
                retVal = retVal.Replace("@", "");
                retVal = retVal.Replace("!", "");
                retVal = retVal.Replace(";", "");
                retVal = retVal.Replace(":", "");
                retVal = retVal.Replace("\\", "");
                retVal = retVal.Replace("%", "");
                retVal = retVal.Replace("insert", "");
                retVal = retVal.Replace("INSERT", "");
                retVal = retVal.Replace("select", "");
                retVal = retVal.Replace("SELECT", "");
                retVal = retVal.Replace("delete", "");
                retVal = retVal.Replace("DELETE", "");
                retVal = retVal.Replace("create", "");
                retVal = retVal.Replace("CREATE", "");
                retVal = retVal.Replace("drop", "");
                retVal = retVal.Replace("DROP", "");
                retVal = retVal.Replace("alter", "");
                retVal = retVal.Replace("ALTER", "");
                retVal = retVal.Replace("or", "");
                retVal = retVal.Replace("OR", "");
                retVal = retVal.Replace("and", "");
                retVal = retVal.Replace("AND", "");
               
            }
            return retVal.ToString();
        }