delphi 学习 SQL 语句 - Select(4): 排序

unit Unit1;
interface
uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls, ExtCtrls, Grids, DBGrids, DB, ADODB;
type
  TForm1 = class(TForm)
    DBGrid1: TDBGrid;
    DataSource1: TDataSource;
    ADODataSet1: TADODataSet;
    Panel1: TPanel;
    Button1: TButton;
    Button2: TButton;
    Button3: TButton;
    Button4: TButton;
    Button5: TButton;
    procedure FormCreate(Sender: TObject);
    procedure Button1Click(Sender: TObject);
    procedure Button2Click(Sender: TObject);
    procedure Button3Click(Sender: TObject);
    procedure Button4Click(Sender: TObject);
    procedure Button5Click(Sender: TObject);
  end;
var
  Form1: TForm1;
implementation
{$R *.dfm}
//根据 Name 字段倒排序
procedure TForm1.Button1Click(Sender: TObject);
begin
  with ADODataSet1 do begin
    Close;
    CommandText := 'SELECT * FROM country ORDER BY Name DESC';
    Open;
  end;
end;
//根据 Name 字段正排序
procedure TForm1.Button2Click(Sender: TObject);
begin
  with ADODataSet1 do begin
    Close;
    CommandText := 'SELECT * FROM country ORDER BY Name ASC';
    Open;
  end;
end;
//根据 Area 字段正排序; 数字字段正排序是: 小-大、反排序是: 大-小
procedure TForm1.Button3Click(Sender: TObject);
begin
  with ADODataSet1 do begin
    Close;
    CommandText := 'SELECT * FROM country ORDER BY Area ASC';
    Open;
  end;
end;
//多个排序条件用 "," 隔开, 排序时先依前者
procedure TForm1.Button4Click(Sender: TObject);
begin
  with ADODataSet1 do begin
    Close;
    CommandText := 'SELECT * FROM country ORDER BY Continent ASC, Capital ASC';
    Open;
  end;
end;
//如果 Where 没有省略, Order By 应该在 Where 后面
procedure TForm1.Button5Click(Sender: TObject);
begin
  with ADODataSet1 do begin
    Close;
    CommandText := 'SELECT * FROM country WHERE Area>200000 ORDER BY Continent ASC';
    Open;
  end;
end;
procedure TForm1.FormCreate(Sender: TObject);
var
  mdbFile: string;
begin
  mdbFile := GetEnvironmentVariable('COMMONPROGRAMFILES');
  mdbFile := mdbFile + '\CodeGear Shared\Data\dbdemos.mdb';
  ADODataSet1.ConnectionString := 'Provider=Microsoft.Jet.OLEDB.4.0;Data Source=' +
    mdbFile + ';Persist Security Info=False';
  DBGrid1.DataSource := DataSource1;
  DataSource1.DataSet := ADODataSet1;
end;
end.