 class Item
        {
            public string VisibleValue;
            public string HiddenValue;
            public Item(string VisibleValue, string HiddenValue)
            {
                this.VisibleValue = VisibleValue;
                this.HiddenValue = HiddenValue;
            }
            public override string ToString()
            {
                return VisibleValue;
            }
        }
        void AddItems(ComboBox box)
        {
            box.Items(new Item(" ", "record_type"));
            box.Items(new Item(" ", "record_number"));
            box.Items(new Item(" ", "record_year"));
            /*
             * ...
             * ...
             * ...
             * ...
             * 
             **/
        }
        object GetField(ComboBox box)
        {
            Item item = (Item)box.SelectedItem;
            string sql = "select " + item.HiddenValue+" from ....";
            /*
            * ...
            * ...
            * ...
            * ...
            * return your result
            **/
        }