added safety div with nullif

mdrozdov/postgresql/dm_course_summary.sql

@@ -5,7 +5,7 @@ select
 	count(distinct e.user_id) as unique_users,
 	count(distinct l.id) as lessons_count,
 	count(distinct lv.id) as total_views,
-	round(count(distinct lv.id)*1.0/count(distinct e.user_id), 2) as avg_views_per_user,
+	round(count(distinct lv.id)*1.0/nullif(count(distinct e.user_id), 0), 2) as avg_views_per_user,
 	min(lv.viewed_at) as first_viewed_at,
 	max(lv.viewed_at) as last_viewed_at
 from enrollments e

mdrozdov/postgresql/dm_platform_summary.sql

@@ -4,5 +4,5 @@ select
 	(select count(id) from courses) as total_courses,
 	(select count(id) from lessons) as total_lessons,
 	(select count(distinct user_id) from lessons_views) as users_with_views,
-	round((select count(id) from lessons)*1.0/(select count(id) from courses), 2) as avg_lessons_per_course,
-	(select count(id) from lessons_views)*1.0/(select count(id) from lessons)
+	round((select count(id) from lessons)*1.0/nullif((select count(id) from courses), 0), 2) as avg_lessons_per_course,
+	round((select count(id) from lessons_views)*1.0/nullif((select count(id) from lessons), 0), 2) as avg_views_per_lesson

mdrozdov/postgresql/dm_user_activity_summary.sql

@@ -19,7 +19,7 @@ with enrollment_counts as(
 	group by user_id
 	order by user_id
 ), engagment_rate as (
-	select tl.user_id, round(v.viewed_lessons_count*100.0/total_lessons, 2) as engagment_rate
+	select tl.user_id, round(v.viewed_lessons_count*100.0/nullif(total_lessons), 2) as engagment_rate
 	from total_lessons tl
 	join views v using(user_id) 
 )