如何在一次连接三个表时求和一列

Question

I believe there is a good way to do. I searched and tried but could not find. I want to join three tables like this (or a better way, please suggest)

SELECT listing.*, users.username, review.rNumber 
     FROM listing, users,review 
WHERE users.uid=listing.cuid and listing.lid=review.lID

But I don't want the review.rNumber I want to get sum of it like sum(rNumber) . Because one listing can have many reviews.. Thank you..

Here is what I want to achieve with this query

1. All the values from listing table.
2. only username from users table
3. sum of reviews from review table

The relation is

• users.uid=listing.cuid and listing.lid=review.lID or
• users.uid=listing.cuid=review.sellerID

Please let me know if I need to add table.. Thanks :)

Answer 1

you can get the sum for user with proper group by but for join with all the listing result you could use a dinamic join

SELECT listing.*, t.username, t.sum_rNumber
fFROM listing
INNER JOIN users   ON users.uid=listing.cuid
INNER JOIN review ON listing.lid=review.lID
INNER JOIN (
      SELECT  users.username as username,  sum( review.rNumber) sum_rNumber
      FROM listing
      INNER JOIN users   ON users.uid=listing.cuid
      INNER JOIN review ON listing.lid=review.lID
      GROUP BY users.username
    ) t on users.username = t.username

(and is more readable the explicit join sintax)