Возвращенные штуки по категориям и каналам за 12 месяцев
SQL, по которому посчитано
SELECT category, channel, SUM(units) AS sold_units, SUM(returned_units) AS returned_units, round(SUM(returned_units) * 1.0 / NULLIF(SUM(units), 0), 3) AS return_rate, round(SUM(returned_revenue)) AS returned_revenue FROM sales WHERE date > (SELECT max(date) FROM sales) - INTERVAL 12 MONTH GROUP BY category, channel HAVING SUM(units) > 0 ORDER BY category, returned_units DESC