How to group datetime by date?

Question

Yii

I have a question, the date is stored in datetime format, I need to do something like this
===10/2/2017===
08:00 message
text 8:20 message text
===10/3/2017===
14:00 message text
15 :00 message text
Approximately grouped like this, but the question arose, how to group only the day of messages?
Comment::find()->groupBy(['date'])->all()
Whether there it is necessary to translate everything into unix date format?

Answer 1

$items = Comment::find()->addSelect(['DATE(date) as just_date'])->asArray()->all();
$items = ArrayHelper::index($items , null, 'just_date');