find_students_with_study_spiral_pattern.sql

Author: stackcats

database/hard/find_students_with_study_spiral_pattern.sql

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+-- Write your PostgreSQL query statement below
+WITH cte AS (
+    SELECT
+        student_id,
+        COUNT(DISTINCT subject)                                                  cycle_length,
+        SUM(hours_studied)                                                       total_study_hours,
+        COUNT(1) OVER (ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING) cnt
+    FROM (
+             SELECT
+                 student_id,
+                 subject,
+                 hours_studied,
+                 session_date::date - (LAG(session_date, 1, session_date)
+                                       OVER (PARTITION BY student_id ORDER BY session_date))::date date_diff
+             FROM study_sessions)
+    GROUP BY student_id
+    HAVING MAX(date_diff) <= 2
+       AND COUNT(DISTINCT subject) >= 3
+       AND COUNT(subject) / COUNT(DISTINCT subject) >= 2)
+SELECT
+    student_id,
+    student_name,
+    major,
+    cycle_length,
+    total_study_hours
+FROM cte
+         LEFT JOIN students USING (student_id)
+WHERE cnt > 1
+ORDER BY cycle_length DESC, total_study_hours DESC