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Average quiz score per course with JOIN and GROUP BY

Combine two tables and summarise the results.

Updated 5 Oct 2026 9 lines 1 min read

JOIN matches each attempt to its course; GROUP BY then gives one row per course with its average.

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SELECT c.title           AS course,
       COUNT(a.id)       AS attempts,
       ROUND(AVG(a.score), 1) AS average_score
FROM courses c
JOIN quiz_attempts a ON a.course_id = c.id
WHERE a.status = 'submitted'
GROUP BY c.id, c.title
HAVING COUNT(a.id) >= 5
ORDER BY average_score DESC;

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