Исправился по всем замечаниям

bhabibullin/postgre/postrge_pet_project.sql

@@ -90,12 +90,10 @@ select
 	count(distinct lv.lesson_id) as viewed_lessons_count,
 	max(lv.viewed_at) as last_view,
 	min(lv.viewed_at) as first_view,
-	round(
-		count(distinct lv.lesson_id) * 100.0 / al.cnt_lesson
-	,2) || '%' as engagegement_rate
+    round(count(distinct lv.lesson_id) * 100.0 / NULLIF(al.cnt_lesson, 0), 4) as engagement_rate
 from users u
 join enrollments e on u.id = e.user_id 
-join lesson_views lv on lv.user_id = u.id 
+left join lesson_views lv on lv.user_id = u.id 
 join available_lessons al on al.user_id = u.id 
 group by u.id, u.name, al.cnt_lesson
 );
@@ -136,7 +134,7 @@ from
 	join lessons l on c.id = l.course_id
 	join enrollments e on e.course_id = c.id 
 	join view_cnt vc on vc.course_id = c.id 
-	join lesson_views lv on lv.lesson_id = l.id
+	left join lesson_views lv on lv.lesson_id = l.id
 group by c.title, vc.cnt, c.id 
 order by course_id
 );
@@ -162,8 +160,8 @@ select
 	count(distinct c.id) as total_courses,
 	count(distinct l.id) as total_lessons,
 	count(distinct lv.user_id) as users_with_views,
-	round(count(distinct l.id) * 1.0 / count(distinct c.id), 2) as avg_lessons_per_course,
-	count(lv.lesson_id) * 1.0 / count(distinct l.id)  as avg_lessons_per_lesson
+	round(count(distinct l.id) * 1.0 / NULLIF(count(distinct c.id), 0), 2) as avg_lessons_per_course,
+	count(lv.lesson_id) * 1.0 / NULLIF(count(distinct l.id), 0) as avg_lessons_per_lesson
 from users u
 left join lesson_views lv on lv.user_id = u.id
 left join lessons l on l.id = lv.lesson_id