// Mission Model
class Mission extends ActiveRecord
{
    public $complete_count;
    public $order_count;
    ...
    public function rules()
    {
        return [[['id', 'count'], 'safe]];
    }

   public function getOrders()
   {
       return $this->hasMany(Order::className(), ['mission_id' => 'id']);
   }
   ....
}

// Order Model
class Order extends ActiveRecord
{
    const STATUS_CREATED = 0;
    const STATUS_COMPLETE = 1
    const STATUS_PROCESSING = 2;
    const STATUS_FAILED = 3
    const STATUS_CANCELED = 4;

    public function rules()
    {
        return [
            [['user', 'mission_id', 'status'], 'safe']
        ];
    }

    public function getMission()
    {
        return $this->hasOne(Mission::className(), ['id' => 'mission_id']);
    }

    public function getUser()
    {
        return $this->hasOne(User::className(), ['id' => 'user']);
    }

    public function find()
    {
        return new OrderQuery(get_called_class());
    }
}

// User Model
class User extends ActiveRecord
{
    public function rules()
    {
        return [['id', 'safe']];
    }
}

// Order Query
class OrderQuery extends ActiveQuery
{
    public function status($status)
    {
        return $this->andWhere(['status' => $status]);
    }
}

// 截止睡觉前想到我的写法
public function actionA()
{
    $missionQuery = Mission::find()->alias('mission');
    $missionQuery->leftJoin(Order::tableName() . ' order', '`order`.mission_id = mission.id');
    // Count Query
    $missionCountQuery = Order::find()->alias('order')->select(new Expression('count(*)'))->where('`order`.mission_id = `mission`.id')->status([Order::STATUS_COMPLETE, Order::STATUS_PROCESSING]);

    // where (select...) < mission.count
    $missionQuery->andWhere('(' . $missionCountQuery->createCommand()->sql . ') < mission.count');

    $data = $missionQuery->all();
    return $data;
}

// 发帖前的写法
public function actionB()
{
    $query = MissionPlatform::find()->alias('p')->select('*')->orderBy('id desc');
    $missionOrderCountQuery = Order::find()->select(['count' => new Expression('count(*)')])->alias('o');
    $missionCompleteCountQuery = clone $missionOrderCountQuery;
    $query->addSelect([
        'order_count' => $missionOrderCountQuery->where('o.mission_id = p.id'),
        'complete_count' => $missionCompleteCountQuery->where('o.mission_id = p.id and o.status in :status', [':status' => [Order::STATUS_COMPLETE, Order::STATUS_PROCESSING]])
    ]);
    // 通过having过滤
    $query->andHaving('complete_count < p.count');
    
    $data = [];
    foreach($query->each(100) as $mission)
    {
        $tmp = $mission->toArray(['id', 'count']);
        $tmp['order_count] = $mission->order_count;
        $tmp['complete_count'] = $mission->complete_count;
        
        $data[] = $tmp;
    }

    return $data;
}

/**
    我承认脑子一抽扔了优雅俩字到帖子标题上 实际却像是跟别人要成品，
    因为发帖的时候刚熬完夜，所以还没整理代码就睡着了，我也是发完才想起来应该扔份代码 
    但是因为自己写的实际代码要比帖子上举例的更复杂(更无用)一点，所以就没贴上，起来发现被喷了，确实是我的不对
    希望各位大佬不要嫌弃小菜给小菜提点建议
    Ps:
        1. 由于本人是个数据库弱痴，所以连查都无从下手的，如果更好的解决办法是关于数据库方面的 希望能不嫌弃丢我两个相关关键词
        2. 关于表关联关系 上述的模型定义应该能看的懂的吧
        3. 我上面的 $missionCountQuery->createCommand()->sql 方式我认为特别不合适。暂时没深入了解这块就没继续改(因为发帖的时候我还在赶这个东西)
        4. rules 定义希望不要吐槽，我实际写模型不会这么写的，只是瞎写一下确保有那么几个字段就好了
**/