SQL Essentials for Data Science

The core verbs

SELECT category, COUNT(*) AS n, AVG(amount) AS avg_amount
FROM orders
WHERE created_at >= '2026-01-01'
GROUP BY category
HAVING COUNT(*) > 10
ORDER BY avg_amount DESC
LIMIT 20;

What each part does

• WHERE filters rows; GROUP BY aggregates; HAVING filters groups.
• JOIN combines tables on a key.
• ORDER BY / LIMIT sort and trim.

Most data work starts with a query like this. Master SELECT/WHERE/GROUP BY/JOIN and you can pull the data you need before any Python touches it.