SQL cheat sheet

Queries, joins and aggregations testers need for data verification.

Query basics

Select + filter

SELECT id, email FROM users WHERE status = 'active';

Sort + limit

ORDER BY created_at DESC LIMIT 10;

Pattern / null

WHERE email LIKE '%@test.io' AND deleted_at IS NULL

Inner join

Only matching rows

FROM orders o JOIN users u ON u.id = o.user_id

Left join

Find orphans with p.id IS NULL

LEFT JOIN payments p ON p.order_id = o.id

Group by

SELECT status, COUNT(*) FROM orders GROUP BY status;

Having

GROUP BY user_id HAVING COUNT(*) > 3;

Duplicates

SELECT email, COUNT(*) FROM users GROUP BY email HAVING COUNT(*) > 1;

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