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?

I started writing a long post on how to design correct ERD diagrams based on the approach from “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.