Question

I have the these tables:

- Users
    - id
- Photos
    - id
    - user_id
- Classifications
    - id
    - user_id
    - photo_id

I would like to order Users by the total number of Photos + Classifications which they own.

I wrote this query:

SELECT users.id, 
COUNT(photos.id) AS n_photo, 
COUNT(classifications.id) AS n_classifications, 
(COUNT(photos.id) + COUNT(classifications.id)) AS n_sum 
FROM users 
LEFT JOIN photos ON (photos.user_id = users.id) 
LEFT JOIN classifications ON (classifications.user_id = users.id) 
GROUP BY users.id 
ORDER BY (COUNT(photos.id) + COUNT(classifications.id)) DESC

The problem is that this query does not work as I expect and returns high numbers while I have only a few photos and classifications in the db. It returns something like this:

id n_photo n_classifications   n_sum
29  19241   19241                   38482
16  16905   16905                   33810
1    431     0                       431
...

Answer 1

You are missing distinct.

  SELECT U.ID, COUNT(DISTINCT P.Id)+COUNT(DISTINCT C.Id) Count
  FROM User U
  LEFT JOIN Photos P ON P.User_Id=U.Id
  LEFT JOIN Classifications C ON C.User_Id=U.Id
  GROUP BY U.Id
  ORDER BY COUNT(DISTINCT P.Id)+COUNT(DISTINCT C.ID)