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Added task 3421
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‎src/main/java/g3401_3500/s3421_find_students_who_improved/readme.md

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3421\. Find Students Who Improved
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Medium
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Table: `Scores`
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+-------------+---------+
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| Column Name | Type |
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+-------------+---------+
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| student_id | int |
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| subject | varchar |
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| score | int |
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| exam_date | varchar |
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+-------------+---------+
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(student_id, subject, exam_date) is the primary key for this table.
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Each row contains information about a student's score in a specific subject on a particular exam date. score is between 0 and 100 (inclusive).
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Write a solution to find the **students who have shown improvement**. A student is considered to have shown improvement if they meet **both** of these conditions:
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* Have taken exams in the **same subject** on at least two different dates
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* Their **latest score** in that subject is **higher** than their **first score**
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Return _the result table_ _ordered by_ `student_id,` `subject` _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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Scores table:
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+------------+----------+-------+------------+
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| student_id | subject | score | exam_date |
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+------------+----------+-------+------------+
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| 101 | Math | 70 | 15-01-2023 |
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| 101 | Math | 85 | 15-02-2023 |
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| 101 | Physics | 65 | 15-01-2023 |
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| 101 | Physics | 60 | 15-02-2023 |
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| 102 | Math | 80 | 15-01-2023 |
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| 102 | Math | 85 | 15-02-2023 |
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| 103 | Math | 90 | 15-01-2023 |
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| 104 | Physics | 75 | 15-01-2023 |
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| 104 | Physics | 85 | 15-02-2023 |
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+------------+----------+-------+------------+
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**Output:**
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+------------+----------+-------------+--------------+
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| student_id | subject | first_score | latest_score |
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+------------+----------+-------------+--------------+
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| 101 | Math | 70 | 85 |
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| 102 | Math | 80 | 85 |
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| 104 | Physics | 75 | 85 |
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+------------+----------+-------------+--------------+
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**Explanation:**
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* Student 101 in Math: Improved from 70 to 85
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* Student 101 in Physics: No improvement (dropped from 65 to 60)
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* Student 102 in Math: Improved from 80 to 85
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* Student 103 in Math: Only one exam, not eligible
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* Student 104 in Physics: Improved from 75 to 85
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Result table is ordered by student\_id, subject.

‎src/main/java/g3401_3500/s3421_find_students_who_improved/script.sql

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# Write your MySQL query statement below
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# #Medium #Database #2025_01_17_Time_466_ms_(74.56%)_Space_0B_(100.00%)
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WITH Ranked AS (
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SELECT
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student_id,
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subject,
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FIRST_VALUE(score) OVER(PARTITION BY student_id,subject ORDER BY exam_date) AS first_score,
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FIRST_VALUE(score) OVER(PARTITION BY student_id,subject ORDER BY exam_date DESC) AS latest_score
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FROM Scores
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)
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SELECT * FROM Ranked
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WHERE first_score<latest_score
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GROUP BY student_id,subject
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ORDER BY student_id,subject

‎src/test/java/g3401_3500/s3421_find_students_who_improved/MysqlTest.java

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package g3401_3500.s3421_find_students_who_improved;
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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 Scores ("
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+ " student_id INT,"
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+ " subject VARCHAR(50),"
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+ " score INT,"
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+ " exam_date VARCHAR(10)"
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+ ");"
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+ "insert into Scores (student_id, subject, score, exam_date) values "
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+ "('101', 'Math', '70', '15-01-2023');"
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+ "insert into Scores (student_id, subject, score, exam_date) values "
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+ "('101', 'Math', '85', '15-02-2023');"
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+ "insert into Scores (student_id, subject, score, exam_date) values "
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+ "('101', 'Physics', '65', '15-01-2023');"
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+ "insert into Scores (student_id, subject, score, exam_date) values "
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+ "('101', 'Physics', '60', '15-02-2023');"
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+ "insert into Scores (student_id, subject, score, exam_date) values "
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+ "('102', 'Math', '80', '15-01-2023');"
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+ "insert into Scores (student_id, subject, score, exam_date) values "
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+ "('102', 'Math', '85', '15-02-2023');"
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+ "insert into Scores (student_id, subject, score, exam_date) values "
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+ "('103', 'Math', '90', '15-01-2023');"
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+ "insert into Scores (student_id, subject, score, exam_date) values "
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+ "('104', 'Physics', '75', '15-01-2023');"
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+ "insert into Scores (student_id, subject, score, exam_date) values "
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+ "('104', 'Physics', '85', '15-02-2023');")
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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/g3401_3500/"
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+ "s3421_find_students_who_improved/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("101"));
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assertThat(resultSet.getNString(2), equalTo("Math"));
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assertThat(resultSet.getNString(3), equalTo("70"));
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assertThat(resultSet.getNString(4), equalTo("85"));
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assertThat(resultSet.next(), equalTo(true));
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assertThat(resultSet.getNString(1), equalTo("102"));
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assertThat(resultSet.getNString(2), equalTo("Math"));
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assertThat(resultSet.getNString(3), equalTo("80"));
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assertThat(resultSet.getNString(4), equalTo("85"));
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assertThat(resultSet.next(), equalTo(true));
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assertThat(resultSet.getNString(1), equalTo("104"));
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assertThat(resultSet.getNString(2), equalTo("Physics"));
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assertThat(resultSet.getNString(3), equalTo("75"));
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assertThat(resultSet.getNString(4), equalTo("85"));
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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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