Author: Alexey Makhotkin squadette@gmail.com. In the first part we’ve designed a logical ERD diagram based on the structured logical model. We built the structured logical model from the free-text business requirements. What if we need to draw a physical ERD diagram for the same task? It turns out that we’ve already done maybe 80% of the work, and we can reuse the structured logical model verbatim. We’ll just use a different graphical notation.

Author: Alexey Makhotkin squadette@gmail.com. I started writing a long post on how to design correct ERD diagrams based on the approach from the “Database Design Book”, but the text got a bit unwieldy. So I’m going to regroup and focus on one part: many-to-many relationships (“M:N links” in book terms). Suppose that you need to build an ERD diagram based on some sort of real-world or teaching task. How do you make sure that your ERD diagram is correct?

Author: Alexey Makhotkin squadette@gmail.com, ~5400 words. This is the first public revision of this text. Early readers have shared encouraging feedback, but I’m sure there’s still room for improvement. I’m releasing it now to gather broader input from a wider audience. Update (2025-06-08): I wrote a prequel to this text: “Multi-join queries design: investigation”. https://minimalmodeling.substack.com/p/multi-join-queries-design-investigation, another 3400 words. Problem Many times I’ve seen people asking for help with fixing some complicated SQL queries.