MySQL 随机连接答案

【问题标题】：MySQL random joinMySQL 随机连接
【发布时间】：2012-11-20 17:52:48
【问题描述】：

这是我的 MySQL 数据库：

我查询所有子类别：

SELECT `a`.`id`, `a`.`name`, `a`.`url_segment`, `a`.`categories_id`, `b`.`image` AS supplements_image
FROM (`subcategories` AS a)
LEFT JOIN `supplements` AS b ON `b`.`subcategories_id` = `a`.`id`
LEFT JOIN `reviews` AS c ON `c`.`supplements_id` = `b`.`id`
GROUP BY `a`.`id`
ORDER BY `a`.`categories_id` ASC, COUNT(c.id) DESC, `b`.`image` ASC

问题在于子类别图片，它应该是该子类别中随机产品的图片，但我总是得到第一个产品的图片。知道我该怎么做吗？

【问题讨论】：

标签： mysql join random

【解决方案1】：

SELECT `a`.`id`, `a`.`name`, `a`.`url_segment`, `a`.`categories_id`, 
        (SELECT `image` 
         FROM `supplements` 
         WHERE `subcategories_id` = `a`.`id` 
         ORDER BY RAND() LIMIT 1
        ) AS supplements_image
FROM (`subcategories` AS a)
LEFT JOIN `reviews` AS c ON `c`.`supplements_id` = `a`.`id`
GROUP BY `a`.`id`
ORDER BY `a`.`categories_id` ASC, COUNT(c.id) DESC

编辑了未指定的别名 b，现在效果很好：See fiddle!

【讨论】：