Поменял форму и названия и исправил NULL

aysat/lifecoding/SQL1.sql

@@ -15,22 +15,23 @@
 Нужно найти ежемесячное процентное изменение месячной аудитории активных пользователей.
 '''
 
-with cte1 as (
-select count(distinct(user_id)) as mau,
+with monthly_users as (
+select count(distinct(user_id)) as active_users,
 date_trunc('month', date) as month
 from abakhytbekuly.users
 group by date_trunc('month', date)
 ),
-cte2 as (
-select mau,
+change as (
+select active_users,
 month,
-lag(mau) over(order by month) as prev_mau
-from cte1
+lag(active_users) over(order by month) as prev_mau
+from monthly_users
 )
-select mau, 
+select active_users, 
 month,
 prev_mau,
-100.0 * (mau - prev_mau) / prev_mau as pct_change
-from cte2   
+100.0 * (active_users - prev_mau) / prev_mau as pct_change -- тут результат странный типа '-66.666666'
+from change
+where prev_mau is not null   
 order by month