Many modern tutorials focus on "how to do X." Gruber focuses on "why X works." The book excels in explaining the set theory behind SQL. It teaches readers to think in sets—a crucial mindset for writing efficient queries. Instead of simply showing the syntax for a SELECT statement, the book delves into how the database engine processes that request, covering the intricacies of data types, table structures, and indexing.
AI can write SQL queries for you. But if you don't understand relational division or Cartesian products , you cannot debug the AI when it goes wrong. Gruber gives you the first-principles thinking that AI cannot replace. Martin Gruber Understanding Sql.pdf