docker ps
CONTAINER ID        IMAGE                COMMAND                CREATED             STATUS              PORTS                    NAMES
e5edc5732d78        mysql:latest         "/entrypoint.sh mysq   49 minutes ago      Up 33 minutes       0.0.0.0:3306->3306/tcp   mysql

docker exec コマンドで接続。

$ docker exec -it e5edc5732d78 bash

$ mysql -u root -p
Enter password:
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 3
Server version: 5.6.24 MySQL Community Server (GPL)

Copyright (c) 2000, 2015, Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql>