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我有两个看起来像这样的表；

   Table: pictures
  `picture_id` int(10) unsigned NOT NULL AUTO_INCREMENT,
  `picture_title` varchar(255) NOT NULL,
  `picture_description` text NOT NULL,
  `picture_src` varchar(50) NOT NULL,
  `picture_filetype` varchar(10) NOT NULL,
  `picture_width` int(11) NOT NULL,
  `picture_height` int(11) NOT NULL,
  `user_id` int(10) unsigned NOT NULL,
  `upload_date` datetime NOT NULL,

--

   Table: picture_votes
  `vote_id` int(10) unsigned NOT NULL AUTO_INCREMENT,
  `picture_id` int(10) unsigned NOT NULL,
  `vote` tinyint(4) NOT NULL,
  `user_id` int(10) unsigned NOT NULL,
  `timestamp` datetime NOT NULL,

我想要做的是从pictures表中选择每个字段，然后计算picture_voteswhere中的所有记录pictures.picture_id = picture_votes.picture_id，例如；

picture_id => 1
picture_title => 'Pic title'
picture_description => 'Pic description'
picture_src => 'b8b3f2c3a85f1a46fbf2ee132d81f783'
picture_filetype => 'jpg'
picture_width => 612
picture_height => 612
user_id => 1
upload_date => '2013-10-12 12:00:00'
vote_count => 3 // Amount of records in `picture_votes` that has `picture_id` = 1

我想出了（$limit要选择的图片数量在哪里）；

SELECT pictures.*, count(picture_votes.vote) as vote_count
    FROM pictures, picture_votes
    WHERE pictures.picture_id = picture_votes.picture_id
    ORDER BY upload_date DESC
    LIMIT $limit

这仅选择 1 张图片和picture_votes.

4

2 回答 2

1

如果picture_id在您的表上建立索引picture_votes，则以下内容可能比连接更快：

SELECT  *
      , ( SELECT COUNT(*) FROM picture_votes WHERE picture_id = pictures.picture_id )
FROM    pictures

这可能会完全跳过表的内容，并允许您简单地计算哈希表中的记录，这应该会更快。

于 2013-10-12T14:07:37.233 回答
1

您真的想使用LEFT join，因为这将返回所有图片，而不仅仅是投票的图片。你也应该做 sum(pv.vote) vs COUNT() 以防你的投票超过 1（嘿，它可能发生！试想：高级帐户 == x2 票 ;-)

SELECT p.*, SUM(pv.vote) votes FROM pictures p
LEFT JOIN picture_votes pv
    ON pv.picture_id=p.picture_id
GROUP BY pv.picture_id

如果您想按前 10 名投票数排序：

SELECT * FROM (
    SELECT p.*, SUM(pv.vote) votes FROM pictures p
    LEFT JOIN picture_votes pv
        ON pv.picture_id=p.picture_id
    GROUP BY pv.picture_id
) AS aggregate
ORDER BY votes DESC
LIMIT 10;
于 2013-10-12T14:03:25.697 回答