LeetCode-in-Java
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.
Solution
# Write your MySQL query statement below
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