LeetCode 1412. Find the Quiet Students in All Exams SQL Solution | Explanation + Code

Description

Table: Student

+---------------------+---------+
| Column Name         | Type    |
+---------------------+---------+
| student_id          | int     |
| student_name        | varchar |
+---------------------+---------+
student_id is the primary key (column with unique values) for this table.
student_name is the name of the student.

 

Table: Exam

+---------------+---------+
| Column Name   | Type    |
+---------------+---------+
| exam_id       | int     |
| student_id    | int     |
| score         | int     |
+---------------+---------+
(exam_id, student_id) is the primary key (combination of columns with unique values) for this table.
Each row of this table indicates that the student with student_id had a score points in the exam with id exam_id.

 

A quiet student is the one who took at least one exam and did not score the highest or the lowest score.

Write a solution to report the students (student_id, student_name) being quiet in all exams. Do not return the student who has never taken any exam.

Return the result table ordered by student_id.

The result format is in the following example.

 

Example 1:

Input: 
Student table:
+-------------+---------------+
| student_id  | student_name  |
+-------------+---------------+
| 1           | Daniel        |
| 2           | Jade          |
| 3           | Stella        |
| 4           | Jonathan      |
| 5           | Will          |
+-------------+---------------+
Exam table:
+------------+--------------+-----------+
| exam_id    | student_id   | score     |
+------------+--------------+-----------+
| 10         |     1        |    70     |
| 10         |     2        |    80     |
| 10         |     3        |    90     |
| 20         |     1        |    80     |
| 30         |     1        |    70     |
| 30         |     3        |    80     |
| 30         |     4        |    90     |
| 40         |     1        |    60     |
| 40         |     2        |    70     |
| 40         |     4        |    80     |
+------------+--------------+-----------+
Output: 
+-------------+---------------+
| student_id  | student_name  |
+-------------+---------------+
| 2           | Jade          |
+-------------+---------------+
Explanation: 
For exam 1: Student 1 and 3 hold the lowest and high scores respectively.
For exam 2: Student 1 hold both highest and lowest score.
For exam 3 and 4: Student 1 and 4 hold the lowest and high scores respectively.
Student 2 and 5 have never got the highest or lowest in any of the exams.
Since student 5 is not taking any exam, he is excluded from the result.
So, we only return the information of Student 2.

Solutions

Solution 1: Using RANK() Window Function + Group By

We can use the RANK() window function to calculate the ascending rank rk1 and descending rank rk2 of each student in each exam, and obtain the table T.

Next, we can perform an inner join between the table T and the table Student, and then group by student ID to obtain the number of times each student has a rank of 1 in ascending order cnt1 and descending order cnt2 in all exams. If both cnt1 and cnt2 are 0, it means that the student is in the middle of the pack in all exams.

sql

# Write your MySQL query statement below WITH T AS ( SELECT student_id, RANK() OVER ( PARTITION BY exam_id ORDER BY score ) AS rk1, RANK() OVER ( PARTITION BY exam_id ORDER BY score DESC ) AS rk2 FROM Exam ) SELECT student_id, student_name FROM T JOIN Student USING (student_id) GROUP BY 1 HAVING SUM(rk1 = 1) = 0 AND SUM(rk2 = 1) = 0 ORDER BY 1;(code-box)