学习 SQL 语句 - Select(6): 字段运算

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;
procedure FormCreate(Sender: TObject);
procedure Button1Click(Sender: TObject);
end;

var
Form1: TForm1;

implementation

{$R *.dfm}

//计算人均面积, 计算支持 + - * / mod
procedure TForm1.Button1Click(Sender: TObject);
begin
with ADODataSet1 do begin
Close;
CommandText := 'SELECT Name, Area / Population AS 人均面积 FROM country';
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.

object Form1: TForm1
Left = 0
Top = 0
Caption = 'Form1'
ClientHeight = 407
ClientWidth = 626
Color = clBtnFace
Font.Charset = DEFAULT_CHARSET
Font.Color = clWindowText
Font.Height = -11
Font.Name = 'Tahoma'
Font.Style = []
OldCreateOrder = False
OnCreate = FormCreate
PixelsPerInch = 96
TextHeight = 13
object DBGrid1: TDBGrid
Left = 0
Top = 33
Width = 626
Height = 374
Align = alClient
DataSource = DataSource1
TabOrder = 0
TitleFont.Charset = DEFAULT_CHARSET
TitleFont.Color = clWindowText
TitleFont.Height = -11
TitleFont.Name = 'Tahoma'
TitleFont.Style = []
end
object Panel1: TPanel
Left = 0
Top = 0
Width = 626
Height = 33
Align = alTop
Caption = 'Panel1'
TabOrder = 1
object Button1: TButton
Left = 6
Top = 5
Width = 75
Height = 25
Caption = 'Button1'
TabOrder = 0
OnClick = Button1Click
end
end
object DataSource1: TDataSource
DataSet = ADODataSet1
Left = 184
Top = 112
end
object ADODataSet1: TADODataSet
CursorType = ctStatic
Parameters = <>
Left = 232
Top = 184
end
end