SELECT * FROM users
WHERE role = 'admin';

DROP TABLE IF EXISTS
  old_sessions;

CREATE INDEX idx_email
ON customers(email);

WITH ranked AS (
  SELECT *, ROW_NUMBER()
  OVER (PARTITION BY dept)
  AS rn FROM employees
)
SELECT * FROM ranked
WHERE rn = 1;

EXPLAIN ANALYZE
SELECT o.id, SUM(price)
FROM orders o
JOIN items i ON o.id=i.order_id
GROUP BY o.id;