$where['_string'] = '`has_number` < `number`';//~~~注意：这里`不能丢了； $coupon_flag = $coupon->where($where)->order('id desc')->field('id,name,type,conditions,price,number,has_number')->select(); 　生成的sql语句：  `id`,`name`,`type`,`conditions`,`price`,`number`,`has_number` FROM `tf_coupon` WHERE ( `has_number` < `number` ) ORDER BY id desc