fixed mistakes

dmedvedev/11.7 Pet Project Additional tasks.sql

@@ -1,14 +1,24 @@
 -- 1. Задание 1: Анализ drop-off точек
 -- Используя conversion_funnel, найди курсы с самым большим процентом отвала между этапами enrolled → started (WHERE stage_name IN (...))
+WITH
+	drop_off
+	AS
+	(
+		SELECT
+			course_id,
+			stage_name,
+			users_count,
+			LAG(users_count) OVER (PARTITION BY course_id) AS prev
+
+		FROM conversion_funnel
+	)
+
 SELECT
 	course_id,
-	stage_name,
-	conversion_from_previous,
-	conversion_from_start
-
-
-FROM conversion_funnel
-WHERE stage_name IN ('started');
+	ROUND(1 - users_count * 1.0 / NULLIF(prev, 0), 2) * 100 || '%' AS percent_of_drop
+FROM drop_off
+WHERE stage_name = 'started'
+ORDER BY percent_of_drop DESC
 
 -- ОТВЕТ: Самые большие проценты отвала между enrolled и started замечены на курсе 1 и 3 (62 и 67% соответственно).