insert into 类问题

   public class Insert
    {
        Hashtable args = new Hashtable();
        string table;        /// <summary>        /// Constructs Insert object        /// </summary>        /// <param name="table">table name to insert to</param>        public Insert(string table)
        {
            this.table = table;
        }        /// <summary>        /// Adds item to Insert object        /// </summary>        /// <param name="name">item name</param>        /// <param name="val">item value</param>        public void Add(string name, object val)
        {
            args.Add(name, val);
        }        /// <summary>        /// Removes item from Insert object        /// </summary>        /// <param name="name">item name</param>        public void Remove(string name)
        {
            try
            {
                args.Remove(name);
            }
            catch
            {
                throw (new Exception("No such item"));
            }
        }        /// <summary>        /// Test representatnion of the Insert object (SQL query)        /// </summary>        /// <returns>System.String</returns>        public override string ToString()
        {
            StringBuilder s1 = new StringBuilder();
            StringBuilder s2 = new StringBuilder();            IDictionaryEnumerator enumInterface = args.GetEnumerator();
            bool first = true;
            while(enumInterface.MoveNext())
            {
                if (first) first = false;
                else 
                {
                    s1.Append(", ");
                    s2.Append(", ");
                }
                s1.Append(enumInterface.Key.ToString());
                s2.Append(enumInterface.Value.ToString());
            }             return "INSERT INTO " + table + " (" + s1 + ") VALUES (" + s2 + ");";
        }        /// <summary>        /// Gets or sets item into Insert object        /// </summary>        object this[string key]
        {
            get
            {
                Debug.Assert(args.Contains(key), "Key not found");
                return args[key];
            }
            set {args[key]=value;}
        }
    }
执行后没有效果
                Insert q = new Insert("考试题型");
                q.Add("考试题型", textBox1.Text.ToString().Trim());
                string sql = q.ToString();
                    MessageBox .Show (sql,"",MessageBoxButtons .OK );