Answers for "how to find out which users have access to mysql database"

mysql show users

select * from mysql.user;
#or for less data
select user, host from mysql.user;

mysql users and privileges list

SELECT * FROM mysql.user;

SELECT * FROM information_schema.user_privileges;
SELECT CONCAT('SHOW GRANTS FOR ''',user,'''@''',host,''';') FROM mysql.user;
SHOW GRANTS FOR 'my_user'@'localhost';