Попросите данные ответить.Проверьте каждый результат.

SELECT
  pr.category,
  ROUND(SUM(s.amount_rub)::numeric, 0) AS revenue,
  ROUND(SUM(s.amount_rub)::numeric, 0)
    - LAG(ROUND(SUM(s.amount_rub)::numeric, 0))
      OVER (PARTITION BY pr.category ORDER BY p.id) AS delta
FROM sales s
JOIN products pr ON pr.id = s.product_id
JOIN periods p ON p.id = s.period_id
JOIN federal_districts fd ON fd.id = s.federal_district_id
WHERE fd.name = 'УРАЛЬСКИЙ ФЕДЕРАЛЬНЫЙ ОКРУГ'
  AND p.period_name IN ('2025, март', '2025, апрель')
GROUP BY pr.category, p.id
ORDER BY delta DESC NULLS LAST
LIMIT 10;