Highest Grade For Each Student

Highest Grade For Each Student

What is this problem about?

The Highest Grade For Each Student coding problem is a database task. You are given an Enrollments table with columns student_id, course_id, and grade. For each student, you need to find their highest grade and the corresponding course. If a student has the same highest grade in multiple courses, you must select the one with the smallest course_id. The final output should be sorted by student_id in ascending order.

Why is this asked in interviews?

Coursera and other data-driven companies use this question to test a candidate's proficiency with Database interview patterns, specifically grouping and ranking. It evaluates whether you can handle tie-breaking scenarios correctly using SQL window functions or subqueries. It also tests your ability to return multiple specific columns from a grouped result, which is a common stumbling block for beginners.

Algorithmic pattern used

This problem is best solved using a Window Function like ROW_NUMBER() or RANK().

1. Partition the data by student_id.
2. Order the rows within each partition by grade in descending order, and then by course_id in ascending order (to handle ties).
3. Assign a row number to each record based on this ordering.
4. Select only the rows where the row number is 1.

Example explanation

Table Enrollments:

student_id	course_id	grade
1	2	95
1	3	95
2	1	80

1. For Student 1: Grades are [95, 95]. Smallest course_id for grade 95 is 2.
2. For Student 2: Grade is 80. course_id is 1. Result: [[1, 2, 95], [2, 1, 80]].

Common mistakes candidates make

• Using MAX() incorrectly: Simply using GROUP BY student_id and MAX(grade) will not necessarily return the correct course_id associated with that grade in all SQL dialects (like MySQL's older versions or standard SQL).
• Ignoring the tie-breaker: Forgetting to sort by course_id when grades are equal.
• Missing the final sort: Not ordering the result set by student_id.

Interview preparation tip

Practice using RANK(), DENSE_RANK(), and ROW_NUMBER(). Understanding the subtle differences between these functions is essential for solving "Top N" problems in SQL. For this specific problem, ROW_NUMBER() is ideal because it guarantees exactly one row per student.