In the end you might think to yourself “why am I doing this, when my SQL database already has query optimisation?”. And it’s a fair question, you are onto it. Try one of those auto-GraphQL things instead. EdgeDB (https://edgedb.com) does it as we speak, runs atop Postgres. Save yourself the enormous effort if you’re only building a GraphQL API for a single RDBMS, and not as a façade for a cluster of microservices and databases and external requests.
Or just nod to your boss and go back to what being a backend developer has always meant: laboriously building by hand completely ad hoc JSON versions of SQL RDBMS schemas, each terribly unhappy in its own way. In no way does doing it manually but presenting GraphQL deviate from this Sisyphean tradition.
I read in the article that NOT having GraphQL exactly match your DB schema is a best practice. My response is “did a backend developer write this?” Sounds awfully convenient for job security!
Is this still true if the structure of the data is relatively simple, but you have tens of millions of users? Say the data that is returned (per user) has 20 or 30 properties in total (for each user), and you are only ever asking for specific data about an individual user.