Question

I am trying to pull a list of last 10 rows whose average rating is above 4. Right now this is done by selecting from the first table and then checking the average if its above 4 then it gets added to a variable if not it does nothing. This is a horrible way to do this especially if there are over 1000 rows.

Here are the two queries:

SELECT * FROM `CLMS_reviews` WHERE id = 465 ORDER BY date DESC

SELECT 
rc.name, rr.rating
FROM `CLMS_reviews_ratings` rr  
LEFT JOIN `CLMS_reviews_categories` rc ON rc.cat_id = rr.cat_id  AND rc.website_id = 465
WHERE rr.review_id = " . $row['id'] . "
GROUP BY rc.name

How can I combine this into one query? I tried this but get an invalid use of GROUP BY:

SELECT 
rr.review_id
FROM `CLMS_reviews` r
LEFT JOIN `CLMS_reviews_ratings` rr ON rr.review_id = r.id
WHERE r.website_id = 465 AND AVG(rr.rating) > 4
GROUP BY rr.review_id LIMIT 10

SOLUTION From below:

SELECT review_id FROM `CLMS_reviews_ratings`
WHERE review_id IN ((SELECT id FROM `CLMS_reviews` WHERE website_id = 465))
GROUP BY review_id
HAVING avg(rating) > 4
LIMIT 10

Answer 1

Cannot test it, but maybe this will do:

SELECT rr.review_id
  FROM `CLMS_reviews` r
  LEFT JOIN `CLMS_reviews_ratings` rr ON rr.review_id = r.id
 WHERE r.website_id = 465
 GROUP BY rr.review_id
HAVING avg(rr.rating) > 4
 LIMIT 10;

If you need to filter on aggregate functions, HAVING is your freiend.