Question

I have a database of three tables: USERS PHOTOS LIKES and a basic outline would be like so:

USERS:
user_id
name


PHOTOS:
photo_id
title
url
user_id

LIKES:
user_id
photo_id

What I want to do is enable a user to like many photos and have photos liked by many users.

Obviously, I want to order these photos by the number of likes, which I can do with a JOIN and COUNT()

What I need to do which I can’t figure out is return the number of ‘likes’ which each photo has. How would I do this?

my current SQL is:

SELECT 
  photos.photo_id,
  photos.title,
  photos.url,
  users.name
FROM photos
LEFT OUTER JOIN users
ON users.user_id = photos.user_id
LEFT OUTER JOIN likes
ON likes.photo_id = photos.photo_id
GROUP BY likes.photo_id
ORDER BY COUNT(*) DESC
LIMIT 20

Answer 1

Just add COUNT(*) to your select list:

SELECT 
  photos.photo_id,
  photos.title,
  photos.url,
  users.name,
  COUNT(*)
FROM photos
LEFT OUTER JOIN users
ON users.user_id = photos.user_id
LEFT OUTER JOIN likes
ON likes.photo_id = photos.photo_id
GROUP BY likes.photo_id
ORDER BY COUNT(*) DESC
LIMIT 20