MySQL group_concat 和计数

Posted 2023-02-24

【中文标题】MySQL group_concat 和计数

【英文标题】：MySQL group_concat and count

【发布时间】：2014-05-25 07:02:58

【问题描述】：

我正在尝试在单个查询中获取每个类别的各个方面，如下所示：

SELECT b.`id` AS parent_id, b.`name` AS parent_name, 
    a.`id` AS child_id, a.`name` AS child_name, a.`pageid` AS t_id, 
    COUNT( c.`id` ) AS deals_in_cat, 
    d.`aspect_values` AS aspects 
        FROM `category_parent` AS a 
        LEFT JOIN `navigation_filters_weightage` AS d ON a.`id` = d.`cat_id`, 
        `deals_parent_cat` AS b, 
        `deals` AS c 
    WHERE a.`parent_id` = b.`id` 
    AND c.`ebaydeals_category` = a.`id` 
        GROUP BY a.`id`, d.`frequency` 
        ORDER BY b.`order` ASC, a.`order` ASC, d.`frequency` DESC;

这个查询给了我以下结果：

如您所见，一个类别（在本例中为手机）的所有方面都位于单独的一行中。我想要的是在一行中获得所有类别的所有方面。所以，我试试这个查询：

SELECT b.`id` AS parent_id, b.`name` AS parent_name, 
    a.`id` AS child_id, a.`name` AS child_name, a.`pageid` AS t_id, 
    COUNT( c.`id` ) AS deals_in_cat, 
    GROUP_CONCAT( DISTINCT d.`aspect_values` ORDER BY d.`frequency` DESC ) AS aspects 
        FROM `category_parent` AS a 
        LEFT JOIN `navigation_filters_weightage` AS d ON a.`id` = d.`cat_id`, 
        `deals_parent_cat` AS b, 
        `deals` AS c 
    WHERE a.`parent_id` = b.`id` 
    AND c.`ebaydeals_category` = a.`id` 
        GROUP BY a.`id` 
        ORDER BY b.`order` ASC , a.`order` ASC;

这给出了以下结果：

如您所见，手机类别的count 有所增加。 Mobiles 只有 271 项，但第二次查询几乎将这个数字乘以编号。该类别的方面。

我不确定为什么会这样。欢迎任何想法。

提前致谢。

【问题讨论】：

我猜你重复了表 c 中的 id 尝试count(DISTINCT c.id )

哦！这么滑！非常感谢@m-khalid-junaid！您能否将其发布为答案，以便我接受。

【参考方案1】：

deals 表中可能有重复的 id 尝试在您的计数函数中使用 DISTINCT

SELECT b.id AS parent_id, 
    b.name AS parent_name, 
    a.id AS child_id,
    a.name AS child_name, 
    a.pageid AS t_id, 
    count(DISTINCT c.id ) AS deals_in_cat ...

【讨论】：

感谢您的快速解决！正在查看错误的列以查找问题。