[dev][nova] How to add a column in table of Nova Database

Hi, I'm a beginner in OpenStack development. I would like to try modifying by adding a property to the 'Instances' database table. But I didn't find description in the documentation of the data model mechanism and how to extend the database. https://docs.openstack.org/nova/latest/ Now, I know that it involves versined object model and alembic. My question is: What is the process of adding a column to a table in the database? Could someone show me the process of modifying a database table or recommend me the relevant documentation Best wishes, Han