Python how migrations work?

Question

Flask

Hello, a small question on migrations, on the principle of their work
Did I understand everything correctly and did it? I work on Flask
I have a database with tables,
I decided to create tables further through migrations
I created a migratyon.py file at the root I
added the code from https://flask-migrate.readthedocs.io/en/latest/
first I did init - it just creates add a folder with migrations
then I do migrate - it creates a version of the migration (as with git commit)
then I do an update - it applies changes to the Base (like git push)
BUT, why when I do all this I delete all other tables created not through migrations?
How to make it so that it does not delete, but only supplements the database with new tables?

Answer 1

Create the first migration and stick the database structure into it.
In order for the migrations to work, there must be a complete history of building the database.