Delphi 与SQL编程(二)(2)

5.2 设计一个数据库查询器　

例17.2：在数据库查询器中，用户可以选择要查询的数据库，查询数据库中的那一个表、根据数据库表中那一个字段进行查询，并且可以方便地指定查询条件，指定查询条件主要包括指定逻辑运算符(=、>、<、<=、>=、like、in、NOT like、NOT in)和字段值。

例子全部的程序**如下：

unit main;

interface

uses

SysUtils, Windows, Messages, Classes, Graphics, Controls,

Forms, Dialogs, StdCtrls, DB, DBTables, Buttons, ComCtrls, Tabnotbk;

type

TQueryForm = class(TForm)

BitBtn1: TBitBtn;

DataSource1: TDataSource;

Table1: TTable;

GroupBox1: TGroupBox;

CheckBox1: TCheckBox;

CheckBox2: TCheckBox;

PageControl1: TPageControl;

TabSheet1: TTabSheet;

Label5: TLabel;

Label1: TLabel;

Label2: TLabel;

Label3: TLabel;

Label4: TLabel;

ListBox1: TListBox;

ListBox2: TListBox;

ListBox3: TListBox;

Edit1: TEdit;

ComboBox1: TComboBox;

BitBtn2: TBitBtn;

TabSheet2: TTabSheet;

Memo1: TMemo;

procedure FormCreate(Sender: TObject);

procedure ListBox1Click(Sender: TObject);

procedure ListBox2Click(Sender: TObject);

procedure BitBtn2Click(Sender: TObject);

end;

var

QueryForm: TQueryForm;

implementation

{$R *.DFM}

uses RSLTFORM;

procedure TQueryForm.FormCreate(Sender: TObject);

begin

Screen.Cursor := crHourglass;

{ Populate the alias list }

with ListBox1 do

begin

Items.Clear;

Session.GetAliasNames(Items);

end;

{ Make sure there are aliases defined }　

Screen.Cursor := crDefault;

if ListBox1.Items.Count < 1 then

MessageDlg( 'There are no database aliases currently defined. You need at least one alias to use this demonstration.',

mtError, [mbOK], 0 );

{ Default the drop-down list to the first value in the list }

ComboBox1.ItemIndex := 0;

end;

procedure TQueryForm.ListBox1Click(Sender: TObject);

var

strValue: string; { Holds the alias selected by the user }

bIsLocal: Boolean; { Indicates whether or not an alias is local }

slParams: TStringList; { Holds the parameters of the selected alias }

iCounter: Integer; { An integer counter variable for loops}

begin

{ Determine the alias name selected by the user }　

with ListBox1 do

strValue := Items.Strings[ItemIndex];　

{ Get the names of the tables in the alias and put them in the appropriate list box, making sure the user's choices are reflected

in the list. }　

ListBox2.Items.Clear;

Session.GetTableNames(strValue, { alias to enumerate }

'', { pattern to match }

CheckBox1.Checked, { show extensions flag }

CheckBox2.Checked, { show system tables flag }

ListBox2.Items); { target for table list }

　

{ Make sure there are tables defined in the alias. If not, show an

error; otherwise, clear the list box. }

　

Screen.Cursor := crDefault;

if ListBox2.Items.Count < 1 then

MessageDlg('There are no tables in the alias you selected. Please

choose another', mtError, [mbOK], 0 );

　

ListBox3.Items.Clear;

end;

　

procedure TQueryForm.ListBox2Click(Sender: TObject);

begin

Screen.Cursor := crHourglass;

try

{ First, disable the TTable object. }

if Table1.Active then

Table1.Close;

{ Open the selected table }　

with ListBox1 do

Table1.DatabaseName := Items.Strings[ItemIndex];　

with ListBox2 do

Table1.TableName := Items.Strings[ItemIndex];　

{ Open the table and put a list of the field names in the Fieldslist box. }