加载对象: 在控制器中 use yii\db\Query;
    $query=new Query();
    查询多条：$arr=$query->select(‘*‘)->from(‘register‘)->where("username=‘jiahaiyong‘")->all();
    查询单条：$arr=$query->select(‘*‘)->from(‘register‘)->where("username=‘jiahaiyong‘")->one();
    限制条数：$query->limit(10);
   两表联查：$query->select([‘user.name AS author‘, ‘post.title as title‘])->from(‘user‘)->leftJoin(‘post‘, ‘post.user_id = user.id‘);
   修改：eg:  $res=Yii::$app-db->createCommand()->update(‘表名‘, 修改数组, " id = $id ")->execute();
   删除：eg:$res=Yii::$app->db->createCommand()->delete(‘表名‘, "id = $id条件")->execute();
   添加eg:$res= Yii::$app->db->createCommand()->insert(‘表名‘,插入的数组)->execute();

yii框架的增删改查