Collecting all ideas (thx @MarcB, @Stephan, @GordonLinoff) the SQL bellows is what I'm looking for:
February
SELECT
SUM(price) AS daySum
FROM
sales
WHERE
date BETWEEN DATE_FORMAT(NOW() - INTERVAL 2 MONTH,'%Y-%m-01 00:00:00') AND DATE_FORMAT(LAST_DAY(NOW() - INTERVAL 2 MONTH),'%Y-%m-%d 23:59:59')
GROUP BY
YEAR(date),
MONTH(date),
DAY(date)
April (we are currently at April month)
SELECT
SUM(price) AS daySum
FROM
sales
WHERE
date BETWEEN DATE_FORMAT(NOW(),'%Y-%m-01 00:00:00') AND DATE_FORMAT(LAST_DAY(NOW()),'%Y-%m-%d 23:59:59')
GROUP BY
YEAR(date),
MONTH(date),
DAY(date)
Thx a lot.