Joins
Two tables walk into a query…
▶ the lesson · ~35s · narrated · tap for sound
the intro
A JOIN combines rows from two tables using a matching column. INNER JOIN keeps only matches, LEFT JOIN keeps every row on the left even without a match. Joins are how normalized data becomes useful answers — and the number one interview topic in SQL.
fun fact ✦
There is even a “self join” — a table joined to itself. Org charts and comment threads run on it.
the docs
quick hits about Joins
15-second answers · interviews, tips, trivia & hidden gems
🎤 interview
INNER vs LEFT JOIN?
📚 tutorial
A join, visualized
💎 deep
A table high-fiving itself
💎 deep
The join everyone calls a bug