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sql/daily_dynamics.sql

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+-- Календарь от первого до последнего факта, отсутствующие дни дают 0.
+-- На пустой БД результат пуст; изменение первого дня NULL (нет предшественника).
+WITH RECURSIVE calendar(day) AS (
+    SELECT MIN(order_date) FROM facts HAVING COUNT(*) > 0
+    UNION ALL
+    SELECT date(day, '+1 day') FROM calendar
+    WHERE day < (SELECT MAX(order_date) FROM facts)
+), totals AS (
+    SELECT order_date, SUM(revenue_kopecks) AS revenue_kopecks
+    FROM daily_category GROUP BY order_date
+), filled AS (
+    SELECT day AS order_date, COALESCE(revenue_kopecks, 0) AS revenue_kopecks
+    FROM calendar LEFT JOIN totals ON totals.order_date = calendar.day
+)
+SELECT order_date, revenue_kopecks,
+       revenue_kopecks - LAG(revenue_kopecks) OVER (ORDER BY order_date)
+           AS change_kopecks
+FROM filled ORDER BY order_date;