with DBGrid1.Columns[0].PickList do
  begin
   Clear;
   Table1.First;
   while not Table1.Eof do
    begin
     Add(Table1.Fields[0].AsString);
     Table1.Next;
    end;
  end;    

 
  object DBLookupComboBox1: TDBLookupComboBox
    Left = 152
    Top = 206
    Width = 145
    Height = 21
    DataField = 'CustNo'
    DataSource = DataSource2
    KeyField = 'CustNo'
    ListField = 'Company'
    ListSource = DataSource1
    TabOrder = 0
  end
  object Table1: TTable
    DatabaseName = 'BCDEMOS'
    TableName = 'customer.db'
    Left = 78
    Top = 138
  end
  object Table2: TTable
    DatabaseName = 'BCDEMOS'
    TableName = 'orders.db'
    Left = 80
    Top = 208
  end
  object DataSource1: TDataSource
    DataSet = Table1
    Left = 138
    Top = 56
  end
  object DataSource2: TDataSource
    DataSet = Table2
    Left = 236
    Top = 66
  end