How to specify SET @var in ActiveRecord?

Question

MySQL

Good afternoon,
here I would like to make a calculation in the request.
Simple query, simple question) How to specify in ActiveRecord SET var := 0;
Thanks

Answer 1

Good evening.

// определяем переменну
public $count_var = 0;
// обращение к переменной
$this->count_var

Answer 2

The solution needs more input. Alternatively, you can group records by the required field and get count(*)