$user=M('User');
$map['id']=array('eq',$_GET['id']);
$user->where($map)->setDec('score');

define ('APP_DEBUG', true);
echo $user->getlastsql();
输出结果：UPDATE `tt_user` SET `score`=score-1 WHERE ( `id` = 1 )

define ('APP_DEBUG', false);
echo $user->getlastsql();
输出结果：UPDATE `tt_user` SET WHERE ( `id` = 1 )