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Added task 3673
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‎src/main/java/g3601_3700/s3673_find_zombie_sessions/readme.md‎

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3673\. Find Zombie Sessions
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Hard
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Table: `app_events`
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+------------------+----------+
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| Column Name | Type |
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+------------------+----------+
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| event_id | int |
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| user_id | int |
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| event_timestamp | datetime |
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| event_type | varchar |
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| session_id | varchar |
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| event_value | int |
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+------------------+----------+
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event_id is the unique identifier for this table.
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event_type can be app_open, click, scroll, purchase, or app_close.
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session_id groups events within the same user session.
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event_value represents: for purchase - amount in dollars, for scroll - pixels scrolled, for others - NULL.
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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:
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* The session duration is **more than** `30` minutes.
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* Has **at least** `5` scroll events.
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* The **click-to-scroll ratio** is less than `0.20` .
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* **No purchases** were made during the session.
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Return _the result table ordered by_ `scroll_count` _in **descending** order, then by_ `session_id` _in **ascending** order_.
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The result format is in the following example.
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**Example:**
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**Input:**
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app\_events table:
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+----------+---------+---------------------+------------+------------+-------------+
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| event_id | user_id | event_timestamp | event_type | session_id | event_value |
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+----------+---------+---------------------+------------+------------+-------------+
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| 1 | 201 | 2024-03-01 10:00:00 | app_open | S001 | NULL |
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| 2 | 201 | 2024-03-01 10:05:00 | scroll | S001 | 500 |
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| 3 | 201 | 2024-03-01 10:10:00 | scroll | S001 | 750 |
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| 4 | 201 | 2024-03-01 10:15:00 | scroll | S001 | 600 |
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| 5 | 201 | 2024-03-01 10:20:00 | scroll | S001 | 800 |
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| 6 | 201 | 2024-03-01 10:25:00 | scroll | S001 | 550 |
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| 7 | 201 | 2024-03-01 10:30:00 | scroll | S001 | 900 |
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| 8 | 201 | 2024-03-01 10:35:00 | app_close | S001 | NULL |
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| 9 | 202 | 2024-03-01 11:00:00 | app_open | S002 | NULL |
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| 10 | 202 | 2024-03-01 11:02:00 | click | S002 | NULL |
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| 11 | 202 | 2024-03-01 11:05:00 | scroll | S002 | 400 |
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| 12 | 202 | 2024-03-01 11:08:00 | click | S002 | NULL |
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| 13 | 202 | 2024-03-01 11:10:00 | scroll | S002 | 350 |
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| 14 | 202 | 2024-03-01 11:15:00 | purchase | S002 | 50 |
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| 15 | 202 | 2024-03-01 11:20:00 | app_close | S002 | NULL |
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| 16 | 203 | 2024-03-01 12:00:00 | app_open | S003 | NULL |
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| 17 | 203 | 2024-03-01 12:10:00 | scroll | S003 | 1000 |
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| 18 | 203 | 2024-03-01 12:20:00 | scroll | S003 | 1200 |
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| 19 | 203 | 2024-03-01 12:25:00 | click | S003 | NULL |
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| 20 | 203 | 2024-03-01 12:30:00 | scroll | S003 | 800 |
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| 21 | 203 | 2024-03-01 12:40:00 | scroll | S003 | 900 |
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| 22 | 203 | 2024-03-01 12:50:00 | scroll | S003 | 1100 |
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| 23 | 203 | 2024-03-01 13:00:00 | app_close | S003 | NULL |
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| 24 | 204 | 2024-03-01 14:00:00 | app_open | S004 | NULL |
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| 25 | 204 | 2024-03-01 14:05:00 | scroll | S004 | 600 |
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| 26 | 204 | 2024-03-01 14:08:00 | scroll | S004 | 700 |
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| 27 | 204 | 2024-03-01 14:10:00 | click | S004 | NULL |
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| 28 | 204 | 2024-03-01 14:12:00 | app_close | S004 | NULL |
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+----------+---------+---------------------+------------+------------+-------------+
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**Output:**
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+------------+---------+--------------------------+--------------+
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| session_id | user_id | session_duration_minutes | scroll_count |
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+------------+---------+--------------------------+--------------+
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| S001 | 201 | 35 | 6 |
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+------------+---------+--------------------------+--------------+
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**Explanation:**
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* **Session S001 (User 201)**:
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* Duration: 10:00:00 to 10:35:00 = 35 minutes (more than 30)
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* Scroll events: 6 (at least 5)
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* Click events: 0
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* Click-to-scroll ratio: 0/6 = 0.00 (less than 0.20)
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* Purchases: 0 (no purchases)
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* S001 is a zombie session (meets all criteria)
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* **Session S002 (User 202)**:
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* Duration: 11:00:00 to 11:20:00 = 20 minutes (less than 30)
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* Has a purchase event
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* S002 is not a zombie session
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* **Session S003 (User 203)**:
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* Duration: 12:00:00 to 13:00:00 = 60 minutes (more than 30)
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* Scroll events: 5 (at least 5)
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* Click events: 1
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* Click-to-scroll ratio: 1/5 = 0.20 (not less than 0.20)
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* Purchases: 0 (no purchases)
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* S003 is not a zombie session (click-to-scroll ratio equals 0.20, needs to be less)
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* **Session S004 (User 204)**:
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* Duration: 14:00:00 to 14:12:00 = 12 minutes (less than 30)
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* Scroll events: 2 (less than 5)
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* S004 is not a zombie session
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The result table is ordered by scroll\_count in descending order, then by session\_id in ascending order.

‎src/main/java/g3601_3700/s3673_find_zombie_sessions/script.sql‎

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# Write your MySQL query statement below
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# #Hard #Database #2025_09_07_Time_278_ms_(100.00%)_Space_0.0_MB_(100.00%)
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SELECT
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session_id,
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user_id,
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TIMESTAMPDIFF(MINUTE, MIN(event_timestamp), MAX(event_timestamp)) AS session_duration_minutes,
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SUM(CASE WHEN event_type = 'scroll' THEN 1 ELSE 0 END) AS scroll_count
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FROM
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app_events
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GROUP BY
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session_id,
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user_id
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HAVING
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TIMESTAMPDIFF(MINUTE, MIN(event_timestamp), MAX(event_timestamp)) > 30
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AND SUM(CASE WHEN event_type = 'scroll' THEN 1 ELSE 0 END) > 4
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AND (
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CAST(SUM(CASE WHEN event_type = 'click' THEN 1 ELSE 0 END) AS DOUBLE) /
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NULLIF(SUM(CASE WHEN event_type = 'scroll' THEN 1 ELSE 0 END), 0)
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) < 0.2
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AND SUM(CASE WHEN event_type = 'purchase' THEN 1 ELSE 0 END) = 0
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ORDER BY
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scroll_count DESC,
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session_id ASC;

‎src/test/java/g3601_3700/s3673_find_zombie_sessions/MysqlTest.java‎

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package g3601_3700.s3673_find_zombie_sessions;
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import static org.hamcrest.CoreMatchers.equalTo;
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import static org.hamcrest.MatcherAssert.assertThat;
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import java.io.BufferedReader;
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import java.io.FileNotFoundException;
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import java.io.FileReader;
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import java.sql.Connection;
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import java.sql.ResultSet;
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import java.sql.SQLException;
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import java.sql.Statement;
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import java.util.stream.Collectors;
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import javax.sql.DataSource;
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import org.junit.jupiter.api.Test;
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import org.zapodot.junit.db.annotations.EmbeddedDatabase;
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import org.zapodot.junit.db.annotations.EmbeddedDatabaseTest;
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import org.zapodot.junit.db.common.CompatibilityMode;
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@EmbeddedDatabaseTest(
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compatibilityMode = CompatibilityMode.MySQL,
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initialSqls =
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"CREATE TABLE app_events ("
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+ " event_id INT PRIMARY KEY,"
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+ " user_id INT NOT NULL,"
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+ " event_timestamp TIMESTAMP NOT NULL,"
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+ " event_type VARCHAR(50) NOT NULL,"
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+ " session_id VARCHAR(50) NOT NULL,"
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+ " event_value INT"
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+ ");"
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+ "INSERT INTO app_events (event_id, user_id, event_timestamp, "
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+ "event_type, session_id, event_value) VALUES"
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+ "(1, 201, '2024-03-01 10:00:00', 'app_open', 'S001', NULL),"
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+ "(2, 201, '2024-03-01 10:05:00', 'scroll', 'S001', 500),"
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+ "(3, 201, '2024-03-01 10:10:00', 'scroll', 'S001', 750),"
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+ "(4, 201, '2024-03-01 10:15:00', 'scroll', 'S001', 600),"
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+ "(5, 201, '2024-03-01 10:20:00', 'scroll', 'S001', 800),"
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+ "(6, 201, '2024-03-01 10:25:00', 'scroll', 'S001', 550),"
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+ "(7, 201, '2024-03-01 10:30:00', 'scroll', 'S001', 900),"
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+ "(8, 201, '2024-03-01 10:35:00', 'app_close', 'S001', NULL),"
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+ "(9, 202, '2024-03-01 11:00:00', 'app_open', 'S002', NULL),"
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+ "(10, 202, '2024-03-01 11:02:00', 'click', 'S002', NULL),"
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+ "(11, 202, '2024-03-01 11:05:00', 'scroll', 'S002', 400),"
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+ "(12, 202, '2024-03-01 11:08:00', 'click', 'S002', NULL),"
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+ "(13, 202, '2024-03-01 11:10:00', 'scroll', 'S002', 350),"
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+ "(14, 202, '2024-03-01 11:15:00', 'purchase', 'S002', 50),"
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+ "(15, 202, '2024-03-01 11:20:00', 'app_close','S002', NULL),"
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+ "(16, 203, '2024-03-01 12:00:00', 'app_open', 'S003', NULL),"
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+ "(17, 203, '2024-03-01 12:10:00', 'scroll', 'S003', 1000),"
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+ "(18, 203, '2024-03-01 12:20:00', 'scroll', 'S003', 1200),"
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+ "(19, 203, '2024-03-01 12:25:00', 'click', 'S003', NULL),"
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+ "(20, 203, '2024-03-01 12:30:00', 'scroll', 'S003', 800),"
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+ "(21, 203, '2024-03-01 12:40:00', 'scroll', 'S003', 900),"
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+ "(22, 203, '2024-03-01 12:50:00', 'scroll', 'S003', 1100),"
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+ "(23, 203, '2024-03-01 13:00:00', 'app_close','S003', NULL),"
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+ "(24, 204, '2024-03-01 14:00:00', 'app_open', 'S004', NULL),"
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+ "(25, 204, '2024-03-01 14:05:00', 'scroll', 'S004', 600),"
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+ "(26, 204, '2024-03-01 14:08:00', 'scroll', 'S004', 700),"
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+ "(27, 204, '2024-03-01 14:10:00', 'click', 'S004', NULL),"
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+ "(28, 204, '2024-03-01 14:12:00', 'app_close','S004', NULL);")
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class MysqlTest {
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@Test
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void testScript(@EmbeddedDatabase DataSource dataSource)
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throws SQLException, FileNotFoundException {
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try (final Connection connection = dataSource.getConnection()) {
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try (final Statement statement = connection.createStatement();
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final ResultSet resultSet =
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statement.executeQuery(
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new BufferedReader(
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new FileReader(
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"src/main/java/g3601_3700/"
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+ "s3673_find_zombie_sessions/"
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+ "script.sql"))
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.lines()
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.collect(Collectors.joining("\n"))
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.replaceAll("#.*?\\r?\\n", ""))) {
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assertThat(resultSet.next(), equalTo(true));
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assertThat(resultSet.getNString(1), equalTo("S001"));
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assertThat(resultSet.getNString(2), equalTo("201"));
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assertThat(resultSet.getNString(3), equalTo("35"));
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assertThat(resultSet.getNString(4), equalTo("6"));
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assertThat(resultSet.next(), equalTo(false));
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}
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}
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}
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}

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