In a relational database, related data lives in separate tables — customers in one, orders in another. Joins are how you bring it back together in a single result, using the keys you met in the Fundamentals module.
You'll learn the main join types and when to use each: INNER JOIN for rows that match on both sides, LEFT and RIGHT JOIN for keeping unmatched rows from one side, and FULL JOIN for keeping everything. You'll also see CROSS JOIN for every combination of rows, and the self join, where a table is joined to itself — useful for things like employee and manager relationships.
Work through the lessons in order, then continue on to Subqueries & CTEs.
A visual introduction to what a join does: how rows from two tables are matched up on a shared key.
A quick, practical tour of the three joins you'll use most often, with examples of each.
A beginner-friendly walkthrough of the four main join types, with queries you can follow along with.
A closer look at LEFT JOIN: what happens to unmatched rows and where NULLs appear in the result.
A fast recap that puts every join type side by side, including cross and self joins.
Goes beyond the everyday joins to cover natural, cross, and self joins and when each one is useful.