Question

I have a table articles, with fields id, rating (an integer from 1-10), and category_id (an integer representing to which category it belongs).

How can I, in one MySQL query, find the single article with the highest rating from each category? ORDER BY and LIMIT would usually be how I would find the top-rated article, I suppose, but I’m not sure how to mix that with grouping to get the desired result, if I even can. (A dependent subquery would likely be an easy answer, but ewwww. Is there something better?)

For the following data:

id | category_id | rating
---+-------------+-------
 1 |           1 |     10
 2 |           1 |      8
 3 |           2 |      7
 4 |           3 |      5
 5 |           3 |      2
 6 |           3 |      6

I would like the following to be returned:

id | category_id | rating
---+-------------+-------
 1 |           1 |     10
 3 |           2 |      7
 6 |           3 |      6

Answer 1

Try These

SELECT id, category_id, rating
FROM   articles a1
WHERE rating = 
(SELECT MAX(a2.rating) FROM articles a2 WHERE a1.category_id = a2.category_id)

OR

SELECT * FROM (SELECT * FROM articles ORDER BY rating DESC) AS a1 GROUP BY a1.rating;