<select name="list">
    <option value="mouse">mouse</option>
    <option value="keyboard">keyboard</option>
    <option value="headphones">headphones</option>
</select>

$list = Yii::$app->request->post('list', 'mouse')

$result =  Yii::$app->getDb()->createCommand('
        Select *
         from order_table
         where items_sort in :list
    ')->bindValue(':list', '('.$list.')')
    ->queryAll();

    return $result;
}

public function actionIndex()
{
    $data = null;
    if(isset($_GET['last_month'])) {

        $data = order::getTest();
    }
    $dataProvider = new ArrayDataProvider([
        'allModels' => $data,
        'sort' => [
        ],
        'pagination' => [
            'pageSize' => 50,
        ],
    ]);

    return $this->render('index',['dataProvider' =>$dataProvider]);

}