学习 SQL 语句 - Select(6): 字段运算

本例效果图:

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代码文件:

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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.


 
   

窗体文件:

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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