You can learn a lot about a system merely by looking at the database schema and data transformations to new consistent data. How exactly these processes do what

You can learn a lot about a system merely by looking at the database schema and data transformations to new consistent data. How exactly these processes do what they do is an implementation detail. Think in invariants, not mental simulation of incidentally complex procedures. In this light knowing SQL is a superpower that applies to all systems built with any RDBMS.