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3673. Find Zombie Sessions
Hard

Table: app_events

+------------------+----------+
| Column Name      | Type     | 
+------------------+----------+
| event_id         | int      |
| user_id          | int      |
| event_timestamp  | datetime |
| event_type       | varchar  |
| session_id       | varchar  |
| event_value      | int      |
+------------------+----------+
event_id is the unique identifier for this table.
event_type can be app_open, click, scroll, purchase, or app_close.
session_id groups events within the same user session.
event_value represents: for purchase - amount in dollars, for scroll - pixels scrolled, for others - NULL.

Write a solution to identify zombie sessions, sessions where users appear active but show abnormal behavior patterns. A session is considered a zombie session if it meets ALL the following criteria:

  • The session duration is more than 30 minutes.
  • Has at least 5 scroll events.
  • The click-to-scroll ratio is less than 0.20 .
  • No purchases were made during the session.

Return the result table ordered by scroll_count in descending order, then by session_id in ascending order.

The result format is in the following example.

 

Example:

Input:

app_events table:

+----------+---------+---------------------+------------+------------+-------------+
| event_id | user_id | event_timestamp     | event_type | session_id | event_value |
+----------+---------+---------------------+------------+------------+-------------+
| 1        | 201     | 2024-03-01 10:00:00 | app_open   | S001       | NULL        |
| 2        | 201     | 2024-03-01 10:05:00 | scroll     | S001       | 500         |
| 3        | 201     | 2024-03-01 10:10:00 | scroll     | S001       | 750         |
| 4        | 201     | 2024-03-01 10:15:00 | scroll     | S001       | 600         |
| 5        | 201     | 2024-03-01 10:20:00 | scroll     | S001       | 800         |
| 6        | 201     | 2024-03-01 10:25:00 | scroll     | S001       | 550         |
| 7        | 201     | 2024-03-01 10:30:00 | scroll     | S001       | 900         |
| 8        | 201     | 2024-03-01 10:35:00 | app_close  | S001       | NULL        |
| 9        | 202     | 2024-03-01 11:00:00 | app_open   | S002       | NULL        |
| 10       | 202     | 2024-03-01 11:02:00 | click      | S002       | NULL        |
| 11       | 202     | 2024-03-01 11:05:00 | scroll     | S002       | 400         |
| 12       | 202     | 2024-03-01 11:08:00 | click      | S002       | NULL        |
| 13       | 202     | 2024-03-01 11:10:00 | scroll     | S002       | 350         |
| 14       | 202     | 2024-03-01 11:15:00 | purchase   | S002       | 50          |
| 15       | 202     | 2024-03-01 11:20:00 | app_close  | S002       | NULL        |
| 16       | 203     | 2024-03-01 12:00:00 | app_open   | S003       | NULL        |
| 17       | 203     | 2024-03-01 12:10:00 | scroll     | S003       | 1000        |
| 18       | 203     | 2024-03-01 12:20:00 | scroll     | S003       | 1200        |
| 19       | 203     | 2024-03-01 12:25:00 | click      | S003       | NULL        |
| 20       | 203     | 2024-03-01 12:30:00 | scroll     | S003       | 800         |
| 21       | 203     | 2024-03-01 12:40:00 | scroll     | S003       | 900         |
| 22       | 203     | 2024-03-01 12:50:00 | scroll     | S003       | 1100        |
| 23       | 203     | 2024-03-01 13:00:00 | app_close  | S003       | NULL        |
| 24       | 204     | 2024-03-01 14:00:00 | app_open   | S004       | NULL        |
| 25       | 204     | 2024-03-01 14:05:00 | scroll     | S004       | 600         |
| 26       | 204     | 2024-03-01 14:08:00 | scroll     | S004       | 700         |
| 27       | 204     | 2024-03-01 14:10:00 | click      | S004       | NULL        |
| 28       | 204     | 2024-03-01 14:12:00 | app_close  | S004       | NULL        |
+----------+---------+---------------------+------------+------------+-------------+

Output:

+------------+---------+--------------------------+--------------+
| session_id | user_id | session_duration_minutes | scroll_count |
+------------+---------+--------------------------+--------------+
| S001       | 201     | 35                       | 6            |
+------------+---------+--------------------------+--------------+

Explanation:

  • Session S001 (User 201):
    • Duration: 10:00:00 to 10:35:00 = 35 minutes (more than 30) 
    • Scroll events: 6 (at least 5) 
    • Click events: 0
    • Click-to-scroll ratio: 0/6 = 0.00 (less than 0.20) 
    • Purchases: 0 (no purchases) 
    • S001 is a zombie session (meets all criteria)
  • Session S002 (User 202):
    • Duration: 11:00:00 to 11:20:00 = 20 minutes (less than 30) 
    • Has a purchase event 
    • S002 is not a zombie session 
  • Session S003 (User 203):
    • Duration: 12:00:00 to 13:00:00 = 60 minutes (more than 30) 
    • Scroll events: 5 (at least 5) 
    • Click events: 1
    • Click-to-scroll ratio: 1/5 = 0.20 (not less than 0.20) 
    • Purchases: 0 (no purchases) 
    • S003 is not a zombie session (click-to-scroll ratio equals 0.20, needs to be less)
  • Session S004 (User 204):
    • Duration: 14:00:00 to 14:12:00 = 12 minutes (less than 30) 
    • Scroll events: 2 (less than 5) 
    • S004  is not a zombie session 

The result table is ordered by scroll_count in descending order, then by session_id in ascending order.

 
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