基于字段的有效性驗證:
procedure TFrom1.aavalidate(sender:TField);
var
 T:ttable;
begin
T:=ttable.create(nil);
t.databasename:=table1.databasename;
t.tablename:=table1.tablename;
t.open;
t.setkey;
t.fieldbyname((sender as Tfield).fieldname).asstring:=(sender as Tfield).value;
if t.getokey then begin //如果在原來的數據表中找到了輸入的數據
 messagedlg('重復',mterror,[mbok],0);
table1.cancel;//取消剛才的輸入
end;
t.close;
t.free;
end;