请问在程序运行中怎么才能给一个表动态的增添或删除字段啊？(0分)

请问在程序运行中怎么才能给一个表动态的增添或删除字段啊？
能否给出实例程序，谢谢！！！

unit Unit1;

interface

uses
Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
Dialogs, StdCtrls, Grids, DBGrids, DB, DBTables;

type
TForm1 = class(TForm)
Button1: TButton;
Database1: TDatabase;
Table1: TTable;
DBGrid1: TDBGrid;
DataSource1: TDataSource;
procedure Button1Click(Sender: TObject);
private
{ Private declarations }
public
{ Public declarations }
end;

var
Form1: TForm1;

implementation

{$R *.dfm}

procedure TForm1.Button1Click(Sender: TObject);
begin
Table1.Close;
Table1.DatabaseName := 'asd';
Table1.TableName:='abc.db';
Table1.FieldDefs.Add('Id',ftString,10);
Table1.FieldDefs.Add('name',ftString,10);
Table1.FieldDefs.Add('age',ftInteger);
Table1.CreateTable;
Table1.Open;
end;

end.

aggree with upper

向表中增加一个 VARCHAR 列：
ALTER TABLE distributors ADD COLUMN address VARCHAR(30);
对现存列改名：
ALTER TABLE distributors RENAME COLUMN address TO city;
删除列：
ALTER TABLE distributors drop COLUMN address