Highest Grade for Each Student
Created: March 4, 2020 by [lek-tin]
Last updated: March 4, 2020
Table: Enrollments
+---------------+---------+
| Column Name | Type |
+---------------+---------+
| student_id | int |
| course_id | int |
| grade | int |
+---------------+---------+
(student_id, course_id) is the primary key of this table.
Write a SQL query to find the highest grade with its corresponding course for each student. In case of a tie, you should find the course with the smallest course_id. The output must be sorted by increasing student_id.
The query result format is in the following example:
Enrollments table:
+------------+-------------------+
| student_id | course_id | grade |
+------------+-----------+-------+
| 2 | 2 | 95 |
| 2 | 3 | 95 |
| 1 | 1 | 90 |
| 1 | 2 | 99 |
| 3 | 1 | 80 |
| 3 | 2 | 75 |
| 3 | 3 | 82 |
+------------+-----------+-------+
Result table:
+------------+-------------------+
| student_id | course_id | grade |
+------------+-----------+-------+
| 1 | 2 | 99 |
| 2 | 2 | 95 |
| 3 | 3 | 82 |
+------------+-----------+-------+
Solution
SELECT student_id,
Min(course_id) AS course_id,
grade
FROM Enrollments
WHERE
(student_id, grade) IN
(
SELECT student_id, MAX(grade)
FROM Enrollments
GROUP BY student_id
ORDER BY NULL
)
GROUP BY student_id
ORDER BY student_id