Hvis du vil returnere et array, skal du bruge en GROUP BY, sådan her
SELECT COUNT(registerTime) as `count` FROM users WHERE DATE(registerTime) = CURDATE() GROUP BY MONTH(registerTime)
Og du kan tilføje et månedsnummer i output for at oprette etiketter
SELECT COUNT(registerTime) as `count`,MONTH(registerTime) as `month` FROM users WHERE DATE(registerTime) = CURDATE() GROUP BY MONTH(registerTime)