Added task 3421

src/main/kotlin/g3401_3500/s3421_find_students_who_improved/readme.md

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+3421\. Find Students Who Improved
+
+Medium
+
+Table: `Scores`
+
+    +-------------+---------+
+    | Column Name | Type    |
+    +-------------+---------+
+    | student_id  | int     |
+    | subject     | varchar |
+    | score       | int     |
+    | exam_date   | varchar |
+    +-------------+---------+
+    (student_id, subject, exam_date) is the primary key for this table.
+    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). 
+
+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:
+
+*   Have taken exams in the **same subject** on at least two different dates
+*   Their **latest score** in that subject is **higher** than their **first score**
+
+Return _the result table_ _ordered by_ `student_id,` `subject` _in **ascending** order_.
+
+The result format is in the following example.
+
+**Example:**
+
+**Input:**
+
+Scores table:
+
+    +------------+----------+-------+------------+
+    | student_id | subject  | score | exam_date  |
+    +------------+----------+-------+------------+
+    | 101        | Math     | 70    | 15-01-2023 |
+    | 101        | Math     | 85    | 15-02-2023 |
+    | 101        | Physics  | 65    | 15-01-2023 |
+    | 101        | Physics  | 60    | 15-02-2023 |
+    | 102        | Math     | 80    | 15-01-2023 |
+    | 102        | Math     | 85    | 15-02-2023 |
+    | 103        | Math     | 90    | 15-01-2023 |
+    | 104        | Physics  | 75    | 15-01-2023 |
+    | 104        | Physics  | 85    | 15-02-2023 |
+    +------------+----------+-------+------------+ 
+
+**Output:**
+
+    +------------+----------+-------------+--------------+
+    | student_id | subject  | first_score | latest_score |
+    +------------+----------+-------------+--------------+
+    | 101        | Math     | 70          | 85           |
+    | 102        | Math     | 80          | 85           |
+    | 104        | Physics  | 75          | 85           |
+    +------------+----------+-------------+--------------+ 
+
+**Explanation:**
+
+*   Student 101 in Math: Improved from 70 to 85
+*   Student 101 in Physics: No improvement (dropped from 65 to 60)
+*   Student 102 in Math: Improved from 80 to 85
+*   Student 103 in Math: Only one exam, not eligible
+*   Student 104 in Physics: Improved from 75 to 85
+
+Result table is ordered by student\_id, subject.

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

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

src/test/kotlin/g3401_3500/s3421_find_students_who_improved/MysqlTest.kt

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+package g3401_3500.s3421_find_students_who_improved
+
+import org.hamcrest.CoreMatchers.equalTo
+import org.hamcrest.MatcherAssert.assertThat
+import org.junit.jupiter.api.Test
+import org.zapodot.junit.db.annotations.EmbeddedDatabase
+import org.zapodot.junit.db.annotations.EmbeddedDatabaseTest
+import org.zapodot.junit.db.common.CompatibilityMode
+import java.io.BufferedReader
+import java.io.FileNotFoundException
+import java.io.FileReader
+import java.sql.SQLException
+import java.util.stream.Collectors
+import javax.sql.DataSource
+
+@EmbeddedDatabaseTest(
+    compatibilityMode = CompatibilityMode.MySQL,
+    initialSqls = [
+        (
+            "    CREATE TABLE Scores (" +
+                "    student_id INT," +
+                "    subject VARCHAR(50)," +
+                "    score INT," +
+                "    exam_date VARCHAR(10)" +
+                ");" +
+                "insert into Scores (student_id, subject, score, exam_date) values " +
+                "('101', 'Math', '70', '15-01-2023');" +
+                "insert into Scores (student_id, subject, score, exam_date) values " +
+                "('101', 'Math', '85', '15-02-2023');" +
+                "insert into Scores (student_id, subject, score, exam_date) values " +
+                "('101', 'Physics', '65', '15-01-2023');" +
+                "insert into Scores (student_id, subject, score, exam_date) values " +
+                "('101', 'Physics', '60', '15-02-2023');" +
+                "insert into Scores (student_id, subject, score, exam_date) values " +
+                "('102', 'Math', '80', '15-01-2023');" +
+                "insert into Scores (student_id, subject, score, exam_date) values " +
+                "('102', 'Math', '85', '15-02-2023');" +
+                "insert into Scores (student_id, subject, score, exam_date) values " +
+                "('103', 'Math', '90', '15-01-2023');" +
+                "insert into Scores (student_id, subject, score, exam_date) values " +
+                "('104', 'Physics', '75', '15-01-2023');" +
+                "insert into Scores (student_id, subject, score, exam_date) values " +
+                "('104', 'Physics', '85', '15-02-2023');"
+            ),
+    ],
+)
+internal class MysqlTest {
+    @Test
+    @Throws(SQLException::class, FileNotFoundException::class)
+    fun testScript(@EmbeddedDatabase dataSource: DataSource) {
+        dataSource.connection.use { connection ->
+            connection.createStatement().use { statement ->
+                statement.executeQuery(
+                    BufferedReader(
+                        FileReader(
+                            "src/main/kotlin/g3401_3500/" +
+                                "s3421_find_students_who_improved/script.sql",
+                        ),
+                    )
+                        .lines()
+                        .collect(Collectors.joining("\n"))
+                        .replace("#.*?\\r?\\n".toRegex(), ""),
+                ).use { resultSet ->
+                    assertThat<Boolean>(resultSet.next(), equalTo<Boolean>(true))
+                    assertThat<String>(resultSet.getNString(1), equalTo<String>("101"))
+                    assertThat<String>(resultSet.getNString(2), equalTo<String>("Math"))
+                    assertThat<String>(resultSet.getNString(3), equalTo<String>("70"))
+                    assertThat<String>(resultSet.getNString(4), equalTo<String>("85"))
+                    assertThat<Boolean>(resultSet.next(), equalTo<Boolean>(true))
+                    assertThat<String>(resultSet.getNString(1), equalTo<String>("102"))
+                    assertThat<String>(resultSet.getNString(2), equalTo<String>("Math"))
+                    assertThat<String>(resultSet.getNString(3), equalTo<String>("80"))
+                    assertThat<String>(resultSet.getNString(4), equalTo<String>("85"))
+                    assertThat<Boolean>(resultSet.next(), equalTo<Boolean>(true))
+                    assertThat<String>(resultSet.getNString(1), equalTo<String>("104"))
+                    assertThat<String>(resultSet.getNString(2), equalTo<String>("Physics"))
+                    assertThat<String>(resultSet.getNString(3), equalTo<String>("75"))
+                    assertThat<String>(resultSet.getNString(4), equalTo<String>("85"))
+                    assertThat<Boolean>(resultSet.next(), equalTo<Boolean>(false))
+                }
+            }
+        }
+    }
+}