Question

I have 3 tables in my mysql DB to query.

• Users_rates (fields: id,userid,raterid,rate,eventid) containing all of the rates(rate) that have been assigned to users(userid), participating to specific events(eventid), by other users(raterid)

• Events_participants (fields:id,userid,eventid) containing all of the users(userid) participating to each event(eventid)

• Users (fields:id,name,lastname)containing all the user relative data

I need to query those three tables to retrieve an event-specific rank for the users’ rates.

Ex. John,Erik and Mark participated to ‘eventid=31’.
John received 1 rate from Mark, and 2 from Erik.
Mark received 1 rate from Erik.
Nobody has rated Erik though.

I need to retrieve for each user name,lastname and the sum of the rates received for eventid=31

I tried with this:

SELECT events_participants.userid,users.name,users.lastname,
(SELECT SUM(rate)FROM users_rates WHERE users_rates.eventid=31 AND users_rates.userid=events_participants.userid)AS rate 
FROM(( events_participants INNER JOIN users ON events_participants.userid=users.id)
LEFT OUTER JOIN users_rates ON events_participants.userid=users_rates.userid )
WHERE events_participants.eventid=31

But I receive:

userid | name | lastname | rate  

1 | luca | silvestro | 1 

3 | claudio | buricchi | 6

3 | claudio | buricchi | 6

What’s the right query?

Thanks

Luca

Answer 1

Try this:

SELECT users.userid, users.name, users.lastname, temp.sum as rate
FROM users LEFT JOIN (
    SELECT userid, SUM(rate) as sum FROM users_rates WHERE eventid = 31 GROUP BY userid
) as temp USING (userid)

It might give an error, this might work instead:

SELECT users.userid, users.name, users.lastname, temp.sum as rate
FROM users, (
    SELECT userid, SUM(rate) as sum FROM users_rates WHERE eventid = 31 GROUP BY userid
) as temp WHERE users.userid = temp.userid