DATABASE

Syntax:
DATABASE()

Returns the default (current) database name as a string in the utf8
character set. If there is no default database, DATABASE() returns
NULL. Within a stored routine, the default database is the database
that the routine is associated with, which is not necessarily the same
as the database that is the default in the calling context.

URL: https://dev.mysql.com/doc/refman/8.0/en/information-functions.html