[Страдалецъ]

Вот вам пример, но лучше делать не через чекбокс, а радиогрупп.

Код:

unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls, DB, Grids, DBGrids, DBClient;

type
  TForm1 = class(TForm)
    ClientDataSet1: TClientDataSet;
    ClientDataSet1Employee: TStringField;
    ClientDataSet1Dismiss: TBooleanField;
    DBGrid1: TDBGrid;
    DataSource1: TDataSource;
    CheckBox1: TCheckBox;
    procedure CheckBox1Click(Sender: TObject);
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

procedure TForm1.CheckBox1Click(Sender: TObject);
begin
 ClientDataSet1.Filtered := False;
 ClientDataSet1.Filter := Format('Dismiss=%d',[Integer(CheckBox1.Checked)]);
 ClientDataSet1.Filtered := True;
end;

end.

дфм-файл

Код:

object Form1: TForm1
  Left = 369
  Top = 113
  Width = 870
  Height = 640
  Caption = 'Form1'
  Color = clBtnFace
  Font.Charset = DEFAULT_CHARSET
  Font.Color = clWindowText
  Font.Height = -11
  Font.Name = 'Tahoma'
  Font.Style = []
  OldCreateOrder = False
  PixelsPerInch = 96
  TextHeight = 13
  object DBGrid1: TDBGrid
    Left = 16
    Top = 104
    Width = 393
    Height = 217
    DataSource = DataSource1
    TabOrder = 0
    TitleFont.Charset = DEFAULT_CHARSET
    TitleFont.Color = clWindowText
    TitleFont.Height = -11
    TitleFont.Name = 'Tahoma'
    TitleFont.Style = []
    Columns = <
      item
        Expanded = False
        FieldName = 'Employee'
        Width = 200
        Visible = True
      end
      item
        Expanded = False
        FieldName = 'Dismiss'
        Visible = True
      end>
  end
  object CheckBox1: TCheckBox
    Left = 24
    Top = 80
    Width = 97
    Height = 17
    Caption = 'Уволенные'
    TabOrder = 1
    OnClick = CheckBox1Click
  end
  object ClientDataSet1: TClientDataSet
    Active = True
    Aggregates = <>
    Params = <>
    Left = 32
    Top = 16
    Data = {
      470000009619E0BD010000001800000002000000000003000000470008456D70
      6C6F7965650100490000000100055749445448020002006400074469736D6973
      7302000300000000000000}
    object ClientDataSet1Employee: TStringField
      FieldName = 'Employee'
      Size = 100
    end
    object ClientDataSet1Dismiss: TBooleanField
      FieldName = 'Dismiss'
    end
  end
  object DataSource1: TDataSource
    DataSet = ClientDataSet1
    Left = 64
    Top = 16
  end
end