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Posted by Junichi Shibatani
Junichi Shibatani
651 Points

Question about GROUP BY

There is a question here: Group all reviews by "movie_id" and get the average "score" and alias it as "average".

Can any one tell why the following answer is wrong?

SELECT movie_id, AVG(score) AS average FROM reviews GROUP BY movie_id;

Thank you.

3 Answers

Bryan Saylor
Bryan Saylor
22,900 Points

When you add movie_id at the beginning you are only selecting one movie. Remove it and it should work.

SELECT AVG(score) AS average FROM reviews GROUP BY movie_id;

Chase Marchione
Chase Marchione
155,055 Points
Chase Marchione
Chase Marchione
155,055 Points

Hi Junichi,

In the first part of your statement, it seems you are also selecting a single movie_id (you'll only need to reference movie_id in your group by clause.) If you remove that, your statement should pass.

SELECT AVG(score) AS average FROM reviews GROUP BY movie_id;

Hope this helps!

Junichi Shibatani
Junichi Shibatani
651 Points

Thank you for your help! It worked.

Junichi Shibatani
Junichi Shibatani
651 Points
Junichi Shibatani
Junichi Shibatani
651 Points

Thank you for your help and explanation. It gives me a chance to go over my understanding/misunderstanding.