SELECT name, list_price
FROM product
WHERE list_price BETWEEN 100 AND 500
  AND name ILIKE '%router%'
  AND active
ORDER BY list_price DESC
LIMIT 20;

• =, <>, <, >, BETWEEN, IN (...), LIKE / ILIKE (case-insensitive in PostgreSQL)
• IS NULL / IS NOT NULL — never = NULL
• DISTINCT removes duplicate rows