学习 SQL 语句 - Select(3): 条件查询与模糊查询

程序员文章站 2024-03-02 20:02:34

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为什么80%的码农都做不了架构师？>>> 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

转载于:https://my.oschina.net/hermer/blog/320487

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