Question

I’ve a vote system which is designed like this:

CREATE TABLE `vote` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `weight` int(11) NOT NULL,
  `submited_date` datetime NOT NULL,
  `resource_type` varchar(255) NOT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=2963832 DEFAULT CHARSET=latin1;

CREATE TABLE `article_preselection_vote` (
  `id` int(11) NOT NULL,
  `article_id` int(11) DEFAULT NULL,
  `user_id` int(11) DEFAULT NULL,
  PRIMARY KEY (`id`),
  KEY `IDX_9B145DEA62922701` (`article_id`),
  KEY `IDX_9B145DEAA76ED395` (`user_id`),
  CONSTRAINT `article_preselection_vote_ibfk_4` FOREIGN KEY (`article_id`) REFERENCES `article` (`id`),
  CONSTRAINT `article_preselection_vote_ibfk_5` FOREIGN KEY (`id`) REFERENCES `vote` (`id`) ON DELETE CASCADE,
  CONSTRAINT `article_preselection_vote_ibfk_6` FOREIGN KEY (`user_id`) REFERENCES `user` (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1;

v.weight can be +1 or -1, I need, given a bunch of articles ID, to get the sum of each positive vote (+1) and the sum of negative vote (-1) per articles id.

Then my result should be

article_id | vote_up | vote_down
-----------|---------|----------
    1      |    36   |     20
-----------|---------|----------
    68     |    12   |     56
-----------|---------|----------
    25     |    90   |     12
-----------|---------|----------

I can get that result by doing the following request, but it’s quite heavy and slow on 2,000,000 votes.

SELECT apv.article_id, COALESCE(SUM(up),0) as up, COALESCE(SUM(down),0) as down 
FROM article_preselection_vote apv 
LEFT JOIN(
    SELECT id, weight up FROM vote WHERE weight > 0 AND vote.resource_type = 'article') v1 ON apv.id = v1.id 
LEFT JOIN(
    SELECT id, weight down FROM vote WHERE weight < 0 AND vote.resource_type = 'article') v2 ON apv.id = v2.id 
WHERE apv.article_id IN (11702,11703,11704,11632,11652,11658)
GROUP BY apv.article_id

Any ideas?

Thanks in advance.

Answer 1

You can try a single join:

SELECT
    apv.article_id,
    SUM(COALESCE(weight, 0) > 0) AS up,
    SUM(COALESCE(weight, 0) < 0) AS down 
FROM article_preselection_vote apv 
LEFT JOIN vote
    ON apv.id = vote.id
    AND vote.resource_type = 'article'
WHERE apv.article_id IN (11702, 11703, 11704, 11632, 11652, 11658)
GROUP BY apv.article_id

If you need to calculate this often it might be worthwhile to denormalize your database and store a cached copy of the results.