为什么我的 MySQL 查询没有正确排序？答案

【问题标题】：Why is my MySQL query not ordering correctly?为什么我的 MySQL 查询没有正确排序？
【发布时间】：2016-06-25 05:07:46
【问题描述】：

在下面的查询中，我尝试按fc.order 升序排列结果：

SELECT *, count(*) AS threads_count FROM (
    SELECT fc.uuid AS category_uuid, fc.name, fc.description, fc.order, fc.icon,
           u.uuid AS user_uuid, u.username, u.avatar
    FROM forum_categories AS fc
    INNER JOIN forum_threads AS ft ON fc.id = ft.forum_category_id
    INNER JOIN users as u ON ft.created_by = u.id
    ORDER BY fc.order ASC, ft.created_at DESC
) AS tmp_table GROUP BY category_uuid

但它似乎不起作用。以下是上述查询的结果截图：

如何按order 列排序结果？

【问题讨论】：

你的外部查询（产生最终结果的那个）没有ORDER BY
必须添加第二条SELECT 声明。

标签： mysql sql rdbms

【解决方案1】：

好的，谢谢大家，但我明白了：

SELECT * FROM (
    SELECT *, count(*) AS threads_count FROM (
        SELECT fc.uuid AS category_uuid, fc.name, fc.description, fc.order, fc.icon,
               u.uuid AS user_uuid, u.username, u.avatar
        FROM forum_categories AS fc
        INNER JOIN forum_threads AS ft ON fc.id = ft.forum_category_id
        INNER JOIN users as u ON ft.created_by = u.id
        ORDER BY ft.created_at DESC
    ) AS t1 GROUP BY category_uuid
) as t2 ORDER BY `order`

【讨论】：

这里不需要嵌套查询，它不仅使查询的可读性降低，而且对性能也有影响。 ORDER BY 在嵌套查询中也没有意义。

【解决方案2】：

SELECT t1.*, count(t1.*) AS threads_count FROM 
 (
        SELECT fc.uuid AS category_uuid, fc.name, fc.description, fc.order, fc.icon,
               u.uuid AS user_uuid, u.username, u.avatar
        FROM forum_categories AS fc
        INNER JOIN forum_threads AS ft ON fc.id = ft.forum_category_id
        INNER JOIN users as u ON ft.created_by = u.id    
 ) AS tmp_table t1 
GROUP BY category_uuid
ORDER BY t1.order ASC, t1.created_at DESC

【讨论】：

您仍然需要嵌套查询的原因并不明显。