If your API needs to serve data that lives in multiple sources, then PostgREST is definitely not the right tool. It is, however, a pretty common design to have

If your API needs to serve data that lives in multiple sources, then PostgREST is definitely not the right tool. It is, however, a pretty common design to have all your data flowing into a database, and being served from there. Indeed, it's probably the simplest and most common design for a basic web application. PostgREST or Hasura can do excellent work there.