[NumLock]

Код:

type
  TForm1 = class(TForm)
    DataSource1: TDataSource;
    DBGrid1: TDBGrid;
    Table1: TTable;
    procedure Table1BeforePost(DataSet: TDataSet);
    procedure Table1BeforeEdit(DataSet: TDataSet);
  private
    { Private declarations }
    F0: String;

procedure TForm1.Table1BeforePost(DataSet: TDataSet);
begin
  if F0<>Table1.Fields[0].AsString then
    ShowMessage('<>');
end;

procedure TForm1.Table1BeforeEdit(DataSet: TDataSet);
begin
  F0:=Table1.Fields[0].AsString;
end;