db:
  image: mysql:5.5
  ports:
    - "3306:3306"
  environment:
    MYSQL_ROOT_PASSWORD: mysql
    MYSQL_USER: userx
    MYSQL_PASSWORD: password
    MYSQL_DATABASE: mydb

GRANT ALL PRIVILEGES ON *.* TO 'userx' with grant option;

FROM mysql:5.5
CMD mysqld && mysql -u root -e "GRANT ALL PRIVILEGES ON *.* TO 'snap' with grant option;"