mysql 将某一列字段乘以$int(整形)比如0.8 就是批量打折的功能

怎么写SQL或者框架语句都可以
下面用原生写的没错吧
$Model = new Model();
$Model->execute("update chi_dish SET dishPrice='dishPrice*$zhekou' WHERE dish_bizNumber='$dish_bizNumber' AND `dishCategory`='$dishCategory'");

//所有价格乘以自己的折扣
$m->where($con)->save(array('dishPrice'=>"dishPrice*$zhekou"));