We have set up the CMS using docker in the google cloud.
After the installation it automatically added a database on its own.
How can I add a table in the database ?
I’m not certain what do you want to add / edit directly in db - in general we do not recommend that, unless you know what you’re doing and perhaps also have backup 
In any case, here is how you can access mysql on docker - How can I run a SQL command when using a Docker Install?