I want to multiply two columns in the yii2 grid the grid view is as follows 

```
<?= GridView::widget([
        //'dataProvider' => $dataProvider,
        'dataProvider'=>new ActiveDataProvider([
          'query' => Adanalytics::find()->
                where(['publisher_id' =>  Yii::$app->user->identity->id ])->
                select('id,ad_id,MAX(impression) AS impression, MAX(view) AS view, MAX(clicks) AS clicks,MAX(cpc) AS cpclick,MAX(cpv) AS cpview, (MAX(clicks)*MAX(cpc)) AS totalccost')->
                groupBy('ad_id, visitor_ip'),
        ]),
        'filterModel' => $searchModel,
        'columns' => [
            ['class' => 'yii\grid\SerialColumn'],

            //'id',
            'ad_id',
            //'advertiser_id',
            //'publisher_id',
            //'visitor_ip',
            //'type_ad',
            'impression',
            'view',
            'clicks',
            //'placed_date',
            //'cpc',
            //'cpv',
            'cpclick',
            'cpview',
            'totalccost',
            //'cpi',

            ['class' => 'yii\grid\ActionColumn'],
        ],
    ]); ?>

```

But it is not giving me the desired output where am I going wrong how can i do this?