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Problem solution · SQL

Find Top Scoring Students

Find Top Scoring Students: a SQL solution using relational aggregation. Learn the idea, check the complexity, and read the full code, with credit to walkccc LeetCode Solutions.

Technique
Relational aggregation
Source
walkccc LeetCode Solutions
Length
29 lines
Start with the idea.

Try the problem first. If you get stuck, read the approach below, then write your own solution. The full code is at the bottom.

Approach

Relational aggregation

For Find Top Scoring Students, the query transforms and combines relational rows, then filters or aggregates them into the requested result.

  1. Identify the source rows and join keys.
  2. Apply filters before aggregation when possible.
  3. Group, rank, or project the final columns required by the result.

Code notes

  • 29 lines of SQL from the credited upstream file 3182.sql.
  • The implementation keeps its working state in language-native values and containers.
  • No explicit loop blocks detected.

Complexity

Review join cardinality, grouping keys, and available indexes when estimating query cost.

Check the problem constraints before deciding whether this complexity will pass.

Source

Code and credit

This code comes from walkccc LeetCode Solutions by P.-Y. Chen (walkccc) and is used under the MIT licence.

Open problem ↗Original source ↗
Full codeFind Top Scoring Students · SQLSQL
Use this to learn the idea, then write your own version.
WITH  Majors AS (    SELECT major, COUNT(course_id) AS course_count    FROM Courses    GROUP BY 1  ),  StudentMetadata AS (    SELECT      Students.student_id,      Students.major,      SUM(        Students.major = Courses.major        AND Enrollments.grade = 'A'      ) AS major_grade_a_count    FROM Students    INNER JOIN Courses      USING (major)    INNER JOIN Enrollments      USING (student_id, course_id)    GROUP BY 1  )SELECT StudentMetadata.student_idFROM StudentMetadataINNER JOIN Majors  ON (    StudentMetadata.major = Majors.major    AND StudentMetadata.major_grade_a_count = Majors.course_count)ORDER BY 1;

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