SQL Tools

Fetch a few columns from one table with a filter.

SELECT id, name, email
FROM users AS u
WHERE u.active = true
ORDER BY u.created_at DESC
LIMIT 25;

Start here: SELECT picks the columns, FROM names the table, and WHERE filters before any sorting. Add ORDER BY and LIMIT to control order and volume.

Combine orders with their customer via a LEFT JOIN.

SELECT o.id, o.total, c.name
FROM orders AS o
LEFT JOIN customers AS c ON c.id = o.customer_id
WHERE o.status = 'paid'
ORDER BY o.total DESC;

A LEFT JOIN keeps every row from the first (FROM) table even with no match, so customers without orders still appear. Use INNER JOIN when you only want matches.

Count orders per customer and keep only the busy ones.

SELECT c.name, COUNT(*) AS order_count
FROM orders AS o
INNER JOIN customers AS c ON c.id = o.customer_id
GROUP BY c.name
HAVING COUNT(*) > 5
ORDER BY order_count DESC;

GROUP BY collapses rows that share the listed column into one. Filter the groups with HAVING — it runs after aggregation, so it can test COUNT(*) or SUM() which WHERE cannot.

Page through rows with ORDER BY and LIMIT + OFFSET.

SELECT id, title, created_at
FROM posts AS p
WHERE p.published = true
ORDER BY p.created_at DESC
LIMIT 20 OFFSET 40;

OFFSET skips rows before LIMIT returns them. Page 3 of 20 rows is LIMIT 20 OFFSET 40. Always pair it with ORDER BY so the same row never shows up on two pages.