dmedvedev/11.5 Pet project Lesson_popularity_ranking.sql

@@ -9,10 +9,11 @@ SELECT
 	table_unique_viewers.unique_v AS unique_viewers,
 	ROUND(AVG(views_one_user_per_one_lesson.views_per_viewer), 2) AS avg_views_per_viewer, --также это можно было посчитать total_views/unique_viewers
 	DENSE_RANK() OVER (
+		PARTITION BY pc.id
 		ORDER BY total_views_lesson.total_views DESC NULLS LAST
 	) AS popularity_rank,
 	
-	ROUND(table_unique_viewers.unique_v * 100.0 / table_enrolled_users.enrolled_to_course, 2) || '%' AS completion_rate
+	ROUND(COALESCE(table_unique_viewers.unique_v, 0) * 100.0 / NULLIF(table_enrolled_users.enrolled_to_course, 0), 2) || '%' AS completion_rate
 	
 	FROM pet_lessons pl
 
@@ -60,5 +61,4 @@ SELECT
 		
 		
 	GROUP BY pl.id, pl.title, pc.id, pc.title, total_views_lesson.total_views, table_unique_viewers.unique_v, table_enrolled_users.enrolled_to_course
-	ORDER BY lesson_id;
-	
+	ORDER BY popularity_rank;