MySQL - Count on a join - mysql

Question

I'm trying to count freelanceFeedback's and order by the count like this:
$sql = "SELECT authentication.*, (SELECT COUNT(*) FROM freelanceFeedback) as taskscount FROM authentication
LEFT JOIN freelanceFeedback
ON authentication.userId=freelanceFeedback.FK_freelanceWinnerUserId
WHERE `FK_freelanceProvider`=$what
ORDER BY taskscount DESC";
But I'm having multiple outputs if the user has multiple feedbacks and it's not ordering by the taskscount.
I can't figure out what the 'tweet' is wrong..
** UPDATE **
I think I've got it myself:
$sql = "SELECT DISTINCT authentication.*,
(SELECT COUNT(*) FROM freelanceFeedback
WHERE FK_freelanceWinnerUserId=userId
) as taskscount
FROM authentication
WHERE `FK_freelanceProvider`=$what
ORDER BY taskscount DESC";
This is only outputting 1 user and ORDERING by the amount of feedbacks.

Answer 1

When you use COUNT(), you also need to use GROUP BY:
SELECT authentication.userId,
COUNT(freelanceFeedback.id) AS taskscount
FROM authentication
LEFT JOIN freelanceFeedback
ON authentication.userId = freelanceFeedback.FK_freelanceWinnerUserId
WHERE `FK_freelanceProvider`= $what
GROUP BY authentication.userId
ORDER BY taskscount DESC
However, this will only work if you are not doing SELECT * (which is bad practice anyway). Everything that's not in the COUNT bit needs to go into GROUP BY. If this includes text fields, you'll not be able to do it, so you'll need to do a JOIN to a subquery. MySQL won't complain if you don't but it can seriously slow things down and other DBs will throw an error, so best to do it right:
SELECT authentication.userId,
authentication.textfield,
authentication.othertextfield,
subquery.taskscount
FROM authentication
LEFT JOIN (SELECT freelanceFeedback.FK_freelanceWinnerUserId,
COUNT(freelanceFeedback.FK_freelanceWinnerUserId) AS taskscount
FROM freelanceFeedback
GROUP BY FK_freelanceWinnerUserId) AS subquery
ON authentication.userId = subquery.FK_freelanceWinnerUserId
WHERE authentication.FK_freelanceProvider = $what
ORDER BY subquery.taskscount DESC
It's not clear what table the FK_freelanceProvider is part of so I've assumed it's authentication.