用联接表求和

Question

Haven't come across a situation like this so not sure how to correct it. I'm guessing a sub query is needed?

I need the SUM of votes.vote and the COUNT of votes.vote . This allows me to calculate a rating (sum of all votes / # of votes = rating) for the location selected.

Here is the query with * and static binding to make it easier to understand :

//prepare
$stmt = $db->prepare("
    SELECT SQL_CALC_FOUND_ROWS
        *,
        COALESCE(SUM(votes.vote),0) AS vote_total,
        COUNT(votes.vote) AS number_votes
    FROM locations
    LEFT JOIN tables
        ON tables.location_id = locations.location_id
    LEFT JOIN votes
        ON votes.location_id = locations.location_id
    LEFT JOIN events
        ON events.location_id = locations.location_id
    WHERE locations.location_id = :location_id
    LIMIT :limit OFFSET :offset
");

//bindings
$binding = array(
    'location_id' => 11,
    'limit' => 20,
    'offset' => 0
);

//execute
$stmt->execute($binding);

//results
$results = $stmt->fetchAll(PDO::FETCH_ASSOC);

There are 11 events joined to this location. There are only two votes joined to it (a value of 3 and a value of 4). I am getting the following :

[vote_total] => 77 (should be 7, but is 7*11)
[number_votes] => 22 (should be 2, but is 2*11)

Aside from that only one result is returned rather than 11. If I remove the votes table join and the SUM/COUNT selects for it all 11 results are shown as they should be.

Is it possible to get the SUM and COUNT totals for votes.vote in the same query in some way or will a separate query be needed just to get those values?

Answer 1

My best guess based on your description of the problem is that you want one row per event. If so:

SELECT SQL_CALC_FOUND_ROWS e.*
       COALESCE(SUM(v.vote), 0) AS vote_total,
       COUNT(v.vote) AS number_votes
FROM locations l LEFT JOIN
     tables
     ON t.location_id = l.location_id LEFT JOIN
     votes v
     ON v.location_id = l.location_id LEFT JOIN
     events e
     ON e.location_id = l.location_id
WHERE l.location_id = :location_id
GROUP BY e.event_id
LIMIT :limit OFFSET :offset;