Igor Belikov

SELECT `name`, COUNT(*) as `c`
FROM `table`
GROUP BY `name`
HAVING `c` > 1

class Department extends \yii\db\ActiveRecord {
  /**
   * @return \yii\db\ActiveQuery
   */
  public function getBuildings() {
    return $this->hasMany(Building::className(), ['department_id' => 'id']);
  }
  // ...
}

class Building extends \yii\db\ActiveRecord {
  /**
   * @return \yii\db\ActiveQuery
   */
  public function getDepartment() {
    return $this->hasOne(Department::className(), ['id' => 'department_id']);
  }
  /**
   * @return \yii\db\ActiveQuery
   */
  public function getRooms() {
    return $this->hasMany(Room::className(), ['building_id' => 'id']);
  }
  // ...
}

var_dump($building->department);
var_dump($building->rooms);

class Room extends \yii\db\ActiveRecord {
  /**
   * @return \yii\db\ActiveQuery
   */
  public function getBuilding() {
    return $this->hasOne(Building::className(), ['id' => 'building_id']);
  }
  // ...
}