This article superbly bridges the (usually very large) gap between Database-Theory and Databases-in-Reality. It'd also be interesting to learn about how MySQL

This article superbly bridges the (usually very large) gap between Database-Theory and Databases-in-Reality. It'd also be interesting to learn about how MySQL and Postgres differ in terms of how they process queries internally. I'm sure there'd be interesting tradeoffs all over the place.