uses
  Forms, Classes, Controls, StdCtrls, Db, DBTables, DBCtrls;


type
  TForm1 = class(TForm)
    Table1: TTable; // DBDemos customer table
    Table2: TTable; // DBDemos orders table
    Button1: TButton;
    DBLookupComboBox1: TDBLookupComboBox;
    DataSource1: TDataSource;
    Table2CustNo: TFloatField; // CustNo key field object used for Lookup
    procedure Button1Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
end;

var
  Form1: TForm1;

implementation

{$R *.DFM}

procedure TForm1.Button1Click(Sender: TObject);
begin
  with TStringField.Create(Table2) do
  begin
    FieldName := 'MyLookup';
    FieldKind:= fkLookup;
    DataSet := Table2;
    name := Dataset.name + FieldName;
    KeyFields:= 'CustNo';
    LookUpDataset:= Table1;
    LookUpKeyFields:= 'CustNo';
    LookUpResultField:= 'Company';
    DbLookupCombobox1.DataField:= FieldName;
    DataSource1.DataSet:= Dataset;
    Table2.FieldDefs.Add(name, ftString, 20, false);
  end;
  DbLookupCombobox1.DataSource:= Datasource1;
  Table1.Active:= True;
  Table2.Active:= True;
end;

end.