学习 SQL 语句 - Select(3): 条件查询与模糊查询
Where 用来指定查询条件;
Like 和 Not Like 来指定模糊条件;
模糊条件中:
_ 表示任一字符;
% 表示任一字符串;
[] 表示一个集合.
本例效果图:
代码文件:
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;
Button6: TButton;
Button7: TButton;
Button8: TButton;
Button9: TButton;
Button10: TButton;
Button11: TButton;
Button12: TButton;
Button13: TButton;
Button14: 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);
procedure Button6Click(Sender: TObject);
procedure Button7Click(Sender: TObject);
procedure Button8Click(Sender: TObject);
procedure Button9Click(Sender: TObject);
procedure Button10Click(Sender: TObject);
procedure Button11Click(Sender: TObject);
procedure Button12Click(Sender: TObject);
procedure Button13Click(Sender: TObject);
procedure Button14Click(Sender: TObject);
end;
var
Form1: TForm1;
implementation
{$R *.dfm}
//country 表中 Area<200000 的记录
procedure TForm1.Button1Click(Sender: TObject);
begin
with ADODataSet1 do begin
Close;
CommandText := 'SELECT * FROM country WHERE Area<200000';
Open;
end;
end;
//country 表中 Continent="South America" 的记录; 字符串值应该在引号中(单引号、双引号均可).
procedure TForm1.Button2Click(Sender: TObject);
begin
with ADODataSet1 do begin
Close;
CommandText := 'SELECT * FROM country WHERE Continent="South America"';
Open;
end;
end;
//country 表中 Name="Cuba" 或者 Name="Peru" 的记录
procedure TForm1.Button3Click(Sender: TObject);
begin
with ADODataSet1 do begin
Close;
CommandText := 'SELECT * FROM country WHERE Name="Cuba" or Name="Peru"';
Open;
end;
end;
//country 表中 Continent="South America" 并且 Area>1000000 的记录
procedure TForm1.Button4Click(Sender: TObject);
begin
with ADODataSet1 do begin
Close;
CommandText := 'SELECT * FROM country WHERE Continent="South America" and Area>1000000';
Open;
end;
end;
//country 表中 Name 是 c 开头的记录; 其中的 % 表示任意字符串
procedure TForm1.Button5Click(Sender: TObject);
begin
with ADODataSet1 do begin
Close;
CommandText := 'SELECT * FROM country WHERE Name LIKE "c%"';
Open;
end;
end;
//country 表中 Name 是 b 或 c 开头的记录; 可以用 "," 隔开更多条件
procedure TForm1.Button6Click(Sender: TObject);
begin
with ADODataSet1 do begin
Close;
CommandText := 'SELECT * FROM country WHERE Name LIKE "[b,c]%"';
Open;
end;
end;
//country 表中 Name 是 a 或 b 或 c 开头的记录
procedure TForm1.Button7Click(Sender: TObject);
begin
with ADODataSet1 do begin
Close;
CommandText := 'SELECT * FROM country WHERE Name LIKE "[a-c]%"';
Open;
end;
end;
//country 表中 Name 不是 a 或 b 或 c 或 m 开头的记录
procedure TForm1.Button8Click(Sender: TObject);
begin
with ADODataSet1 do begin
Close;
CommandText := 'SELECT * FROM country WHERE Name NOT LIKE "[a-c,m]%"';
Open;
end;
end;
//country 表中 Name 不是 a 或 b 或 c 开头的记录
procedure TForm1.Button9Click(Sender: TObject);
begin
with ADODataSet1 do begin
Close;
CommandText := 'SELECT * FROM country WHERE Name NOT LIKE "[a-c]%"';
Open;
end;
end;
//country 表中 Name 包含 er 的记录
procedure TForm1.Button10Click(Sender: TObject);
begin
with ADODataSet1 do begin
Close;
CommandText := 'SELECT * FROM country WHERE Name LIKE "%er%"';
Open;
end;
end;
//country 表中 Name 包含空格的记录
procedure TForm1.Button11Click(Sender: TObject);
begin
with ADODataSet1 do begin
Close;
CommandText := 'SELECT * FROM country WHERE Name LIKE "% %"';
Open;
end;
end;
//country 表中 Name 第二个字符任意, 但第一字符是 p、第三字符是 r 的记录; "_" 表示任意字符
procedure TForm1.Button12Click(Sender: TObject);
begin
with ADODataSet1 do begin
Close;
CommandText := 'SELECT * FROM country WHERE Name LIKE "p_r%"';
Open;
end;
end;
//country 表中 Name 是 4 个字符的记录
procedure TForm1.Button13Click(Sender: TObject);
begin
with ADODataSet1 do begin
Close;
CommandText := 'SELECT * FROM country WHERE Name LIKE "____"';
Open;
end;
end;
//country 表中 Name 是 4 个字符, 但最后是 a 结尾的记录
procedure TForm1.Button14Click(Sender: TObject);
begin
with ADODataSet1 do begin
Close;
CommandText := 'SELECT * FROM country WHERE Name LIKE "___a"';
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:
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 = 65
Width = 626
Height = 342
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 = 65
Align = alTop
Caption = 'Panel1'
TabOrder = 1
object Button1: TButton
Left = 6
Top = 5
Width = 75
Height = 25
Caption = 'Button1'
TabOrder = 0
OnClick = Button1Click
end
object Button2: TButton
Left = 87
Top = 5
Width = 75
Height = 25
Caption = 'Button2'
TabOrder = 1
OnClick = Button2Click
end
object Button3: TButton
Left = 168
Top = 5
Width = 75
Height = 25
Caption = 'Button3'
TabOrder = 2
OnClick = Button3Click
end
object Button4: TButton
Left = 249
Top = 5
Width = 75
Height = 25
Caption = 'Button4'
TabOrder = 3
OnClick = Button4Click
end
object Button5: TButton
Left = 330
Top = 5
Width = 75
Height = 25
Caption = 'Button5'
TabOrder = 4
OnClick = Button5Click
end
object Button6: TButton
Left = 411
Top = 5
Width = 75
Height = 25
Caption = 'Button6'
TabOrder = 5
OnClick = Button6Click
end
object Button7: TButton
Left = 492
Top = 5
Width = 75
Height = 25
Caption = 'Button7'
TabOrder = 6
OnClick = Button7Click
end
object Button8: TButton
Left = 6
Top = 36
Width = 75
Height = 25
Caption = 'Button8'
TabOrder = 7
OnClick = Button8Click
end
object Button9: TButton
Left = 87
Top = 36
Width = 75
Height = 25
Caption = 'Button9'
TabOrder = 8
OnClick = Button9Click
end
object Button10: TButton
Left = 168
Top = 36
Width = 75
Height = 25
Caption = 'Button10'
TabOrder = 9
OnClick = Button10Click
end
object Button11: TButton
Left = 249
Top = 36
Width = 75
Height = 25
Caption = 'Button11'
TabOrder = 10
OnClick = Button11Click
end
object Button12: TButton
Left = 330
Top = 34
Width = 75
Height = 25
Caption = 'Button12'
TabOrder = 11
OnClick = Button12Click
end
object Button13: TButton
Left = 411
Top = 36
Width = 75
Height = 25
Caption = 'Button13'
TabOrder = 12
OnClick = Button13Click
end
object Button14: TButton
Left = 492
Top = 36
Width = 75
Height = 25
Caption = 'Button14'
TabOrder = 13
OnClick = Button14Click
end
end
object DataSource1: TDataSource
DataSet = ADODataSet1
Left = 184
Top = 112
end
object ADODataSet1: TADODataSet
CursorType = ctStatic
Parameters = <>
Left = 232
Top = 184
end
end