Students And Examinations

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Students And Examinations

Compute each student's exam attendance across multiple subjects, including subjects with zero attempts.

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Problem Statement

You are given three tables describing students, subjects, and examination records. For every student, report how many times they took each subject exam.

A student should appear once for every subject, even if they never took that exam. The result should include the student's ID, name, subject name, and the number of attended exams.

Return the rows ordered by student ID, then subject name.

Input Format

A table of students with columns such as student_id and student_name.
A table of subjects with columns such as subject_name.
A table of examination records with columns such as student_id and subject_name.

Each row in the exam table represents one exam attendance.

Output Format

Return one row per (student, subject) pair with:

student ID
student name
subject name
attended exam count

Constraints

Every student must be paired with every subject.
Counts may be zero.
Sorting should be deterministic by student ID and subject name.
Assume input tables may contain multiple exam rows for the same student and subject.

Examples

Sample cases returned by the problem API.

Example 1

Input

Students
| student_id | student_name |
|-----------:|--------------|
| 1          | Alice        |
| 2          | Bob          |

Subjects
| subject_name |
|--------------|
| Math         |
| Physics      |

Examinations
| student_id | subject_name |
|-----------:|--------------|
| 1          | Math         |
| 1          | Math         |
| 1          | Physics      |
| 2          | Math         |

Output

| student_id | student_name | subject_name | attended_exams |
|-----------:|--------------|--------------|----------------:|
| 1          | Alice        | Math         | 2               |
| 1          | Alice        | Physics      | 1               |
| 2          | Bob          | Math         | 1               |
| 2          | Bob          | Physics      | 0               |

Explanation

Generate all student-subject combinations, then count how many examination rows match each pair. Bob never took Physics, so his count is 0.

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