True blue/green deployments with databases is nearly impossible. Usually application code is tightly coupled to the database. So it is not possible to deploy or rollback separately.
The main method of accomplishing this in databases is by making sure your changes are backwards compatible. It take a lot more work from devs to make sure this happens.
I suggest you read this:
https://learn.microsoft.com/en-us/answers/questions/159546/sql-server-zero-downtimeblue-green-deployment.html