Ivanbyone · Ivanbyone · Jul 20, 2025 · Jul 20, 2025
diff --git a/README.md b/README.md
@@ -183,6 +183,7 @@ Useful for preparing for technical interviews and improving your SQL skills.
     - [1907. Count Salary Categories](./leetcode/medium/1907.%20Count%20Salary%20Categories.sql)
     - [1934. Confirmation Rate](./leetcode/medium/1934.%20Confirmation%20Rate.sql)
     - [3220. Odd and Even Transactions](./leetcode/medium/3220.%20Odd%20and%20Even%20Transactions.sql)
+    - [3421. Find Students Who Improved](./leetcode/medium/3421.%20Find%20Students%20Who%20Improved.sql)
     - [3475. DNA Pattern Recognition](./leetcode/medium/3475.%20DNA%20Pattern%20Recognition.sql)
     - [3497. Analyze Subscription Conversion](./leetcode/medium/3497.%20Analyze%20Subscription%20Conversion.sql)
     - [3601. Find Drivers with Improved Fuel Efficiency](./leetcode/medium/3601.%20Find%20Drivers%20with%20Improved%20Fuel%20Efficiency.sql)

diff --git a/leetcode/medium/3421. Find Students Who Improved.sql b/leetcode/medium/3421. Find Students Who Improved.sql
@@ -0,0 +1,74 @@
+/*
+Question 3421. Find Students Who Improved
+Link: https://leetcode.com/problems/find-students-who-improved/description/?envType=problem-list-v2&envId=database
+
+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.
+*/
+
+WITH first_scores AS (
+    SELECT
+        student_id,
+        subject,
+        FIRST_VALUE(score) OVER (PARTITION BY student_id, subject ORDER BY exam_date ASC) AS first_score
+    FROM Scores
+),
+
+last_scores AS (
+    SELECT
+        student_id,
+        subject,
+        FIRST_VALUE(score) OVER (PARTITION BY student_id, subject ORDER BY exam_date DESC) AS latest_score
+    FROM Scores
+),
+
+exams AS (
+    SELECT
+        student_id,
+        subject
+    FROM Scores
+    GROUP BY student_id, subject
+),
+
+all_scores AS (
+    SELECT 
+        e.student_id,
+        e.subject,
+        (
+            SELECT fs.first_score
+            FROM first_scores AS fs
+            WHERE fs.student_id = e.student_id AND fs.subject = e.subject
+            LIMIT 1
+        ) AS first_score,
+        (
+            SELECT ls.latest_score
+            FROM last_scores AS ls
+            WHERE ls.student_id = e.student_id AND ls.subject = e.subject
+            LIMIT 1
+        ) AS latest_score
+    FROM exams AS e
+)
+
+SELECT
+    student_id,
+    subject,
+    first_score,
+    latest_score
+FROM all_scores
+WHERE latest_score > first_score
+ORDER BY student_id, subject