fix mistakes

dmedvedev/11.7 Pet Project Additional tasks.sql

@@ -1,24 +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
-	)
-
+WITH drop_off AS (
+    SELECT
+        course_id,
+        stage_name,
+        users_count,
+        LAG(users_count) OVER (
+            PARTITION BY course_id 
+            ORDER BY stage_name
+        ) AS prev
+    FROM conversion_funnel
+    WHERE stage_name IN ('enrolled', 'started') 
+)
 SELECT
-	course_id,
-	ROUND(1 - users_count * 1.0 / NULLIF(prev, 0), 2) * 100 || '%' AS percent_of_drop
+    course_id,
+    ROUND((1 - users_count * 1.0 / NULLIF(prev, 0)) * 100, 2) || '%' AS percent_of_drop
 FROM drop_off
 WHERE stage_name = 'started'
-ORDER BY percent_of_drop DESC
+ORDER BY (1 - users_count * 1.0 / NULLIF(prev, 0)) DESC;
+
 
 -- ОТВЕТ: Самые большие проценты отвала между enrolled и started замечены на курсе 1 и 3 (62 и 67% соответственно).