In many projects the database is way more important than the "backend" or what have you. Business logic in SQL (DB table schemas is 80% of business logic anyway

In many projects the database is way more important than the "backend" or what have you. Business logic in SQL (DB table schemas is 80% of business logic anyway...); Java or Python or whatever is just some glue to connect user interface or API to database. (I think "glue code" in parent referred to "what is not the UI or DB" BTW, i.e. the "Java app".) When the database is the most fundamental thing, then trying to abstract away the database can be a bit like trying to abstract away the programming language you are using. I have code where I would much rather rewrite the "backend" in another language than swap out the database. I think it was a very good analogy to say that abstracting over database is a bit like abstracting over what programming language you are using.