It took me quite some time before I could reason efficiently about SQL JOINs. And I must admit, the set theory diagrams never helped me really understand JOINs in SQL. So today, I want to help you understand JOINs in a different way, hoping to make the concept click at once for you too!

If you’re like me, understanding SQL is taking you a long time. And some efforts. It took me years to get a good mental model of how SQL queries are implemented, and then up from the lower levels, to build a mental model of how to reason in SQL.

Nowadays, in most case, I can think in terms of SQL and write queries that will give me the result set I need. In most cases, because some parts of SQL are still complex, and I don’t practice as much as I used to. In particular, newer PostgreSQL features are areas I still need to work with more before I can integrate them in my daily workflow.

Today, I want to introduce the central concept of the SQL language. What is an SQL relation?