Add YTD total to fct_monthly_active_students (#242)

dbt/models/marts/metrics/_metrics__models.yml

@@ -22,6 +22,9 @@ models:
       description: the number of active students on given month, in given country
       data_tests:
         - not_null 
+
+    - name: num_active_students_ytd
+      description: the number of unique students as a rolling total for each school year
 
     data_tests:
       - dbt_utils.unique_combination_of_columns:

dbt/models/marts/metrics/fct_monthly_active_students.sql

@@ -1,25 +1,82 @@
-{# 
-    model: fct_active_students_monthly
-    changelog:
-    author      version date        comments
-    js          2.0    2024-09-17   init 
-    ""          2.1     ""          removing anonymous users from scope
-#}
-
-with active_students as (
-    select * 
+-- Step 0: Stage data
+with 
+active_students as (
+    select 
+        *, 
+        date_trunc('month', activity_date) as activity_month 
     from {{ ref('dim_active_students') }}
 ),
 
+first_active_month as (
+    select 
+        student_id, 
+        school_year,
+        min(activity_month) as first_activity_month 
+    from active_students
+    group by student_id, school_year
+),
+
+combined as (
+    select 
+        acs.school_year,
+        acs.activity_month,
+        acs.us_intl,
+        acs.country,
+        acs.student_id
+    from active_students as acs 
+    left join first_active_month as fam 
+         on acs.student_id = fam.student_id 
+        and acs.school_year = fam.school_year
+        and acs.activity_month >= fam.first_activity_month
+),
+
 final as (
     select 
-        date_trunc('month',activity_date) as activity_month,
+        com.school_year,
+        com.activity_month,
+        com.us_intl,
+        com.country,
+        count(distinct com.student_id) as num_active_students,
+        count(distinct case 
+            when com.activity_month = fam.first_activity_month
+            then com.student_id end) as num_new_students
+    from combined as com
+    left join first_active_month as fam 
+        on com.student_id = fam.student_id 
+        and com.school_year = fam.school_year
+    group by com.school_year, com.activity_month, com.us_intl, com.country
+),
+
+rolling_final_prep as (
+    select 
+        school_year,
+        activity_month,
         us_intl,
         country,
-        count(distinct student_id) as num_active_students
-    from active_students
-    {{ dbt_utils.group_by(3) }} )
-
+        num_active_students,
+        num_new_students
+    from final
+),
+
+rolling_final as (
+    select 
+        school_year,
+        activity_month,
+        us_intl,
+        country,
+        num_active_students,
+        sum(num_new_students) over (
+            partition by 
+                school_year, 
+                us_intl, 
+                country
+            order by activity_month
+            rows between unbounded preceding and current row
+        ) as num_active_students_ytd
+    from rolling_final_prep )
+
 select * 
-from final 
-order by activity_month desc 
+from rolling_final
+order by 
+    school_year, 
+    activity_month desc