Syntax:
DAYOFMONTH(date)

Returns the day of the month for date, in the range 1 to 31, or 0 for
dates such as '0000-00-00' or '2008-00-00' that have a zero day part.
Returns NULL if date is NULL.

URL: https://dev.mysql.com/doc/refman/8.0/en/date-and-time-functions.html

