$query = $builder->select('log')
            ->count('offerId')
            ->setColumns(['errorCode', 'errorMessage'])
            ->groupBy(['errorCode', 'errorMessage'])
            ->where()
            ->equals('offerId', $this->offerId)
            ->equals('date', $this->date)
            ->end();

_-------------------_
SELECT COUNT(offerId), errorCode, errorMessage FROM log WHERE offerId = 'test' AND date = '2019-02-12' GROUP BY errorCode, errorMessage