Yii createCommand不会返回正确的结果

Question

I am trying to get a random ID from a table with a specific visiblity=2 clause but I am having issues getting it to return the ID, it says Undefined index: id.

     $space = Yii::app()->db->createCommand()
         ->select('id')
         ->from('space')
         ->where('id=rand() AND visibility=2')
         ->limit(1)
         ->queryAll();
         //->queryRow();
     echo $space['id'];

Is his not the correct way?

I figured out another solution using the already loaded info from my original version without guest check.

    $max = Space::model()->count();
    $randId = rand(0,$max);
    $space = Space::model()->find(array('offset'=>$randId));
    if ($space->attributes['visibility'] == 2) {

Answer 1

You can use ORDER BY RAND() instead of id = rand(). Also you can use ->queryScalar() to get only ID directly.

$space = Yii::app()->db->createCommand()
     ->select('id')
     ->from('space')
     ->where('visibility = 2')
     ->order('RAND()')
     ->limit(1)
     ->queryScalar();

 echo $space;

Keep in mind that RAND() is slow solution. Check alternatives.
Also, if you get no entries from database, you have to check that case:

if (!empty($space)) { // id will never be 0
    // Do something with $space
} else {
    throw new CHttpException(404, 'No data found');
}