PURCHASE

The Art of PostgreSQL, one article at a time

The Art of PostgreSQL blog introduces PostgreSQL concepts that are useful for application developers. The content of this blog is either extracted from the published book, or written in preparation for book material. Reading this blog, you can enjoy The Art of PostgreSQL content one piece at a time!

Remember to practice what you learn here and elsewhere!

2019-09-07

What is an SQL JOIN?

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! As we saw in the previous article What is an SQL relation?, in SQL a relation is a collection of objects, all sharing the same definition.

2019-09-07

What is an SQL relation?

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.