mysql – 按组排序数据

2024年1月5日 205次阅读

数据集：

id  uid     activity    postid  
1   20      A           1
2   20      A           1
3   6       A           1
4   3       A           1
5   6       A           1
6   13      A           1
7   13      B           1
8   18      B           1
9   18      B           1
10  1       A           1

目前的结果：

id  uid     uid_list        groupCount  activity    postid
9   18      18,13           3           B           1
1   20      1,13,6,3,20     7           A           1

预期成绩：

id  uid     uid_list        groupCount  activity    postid
9   18      18,13           3           B           1
10  1       1,13,6,3,20     7           A           1

我的查询：

SELECT
    id,
    uid,
    GROUP_CONCAT(DISTINCT uid ORDER BY id DESC) as uid_list,
    COUNT(*) as groupCount,
    activity,
    postid
FROM (
    SELECT *
    FROM `user_activities`
    ORDER BY id DESC) as tbl
GROUP BY
    activity, postid
ORDER BY
    id DESC

我希望按活动和postid分组,同时按id降序排列结果.并希望为每个群体拥有最新的id和uid.我不明白为什么这个查询不返回预期的输出.

最佳答案 据我所知,id值正在增加.要获取最新值,可以使用聚合函数MAX().

此外,您的内部查询与排序是不必要的,因为引擎必须在构建GROUP_CONCAT()的结果时按id对结果集进行排序.

要检索特定id列的uid,您需要自联接到同一个表.

SELECT
    a.id, b.uid, a.uid_list, a.groupcount, a.activity, a.postid
FROM (
    SELECT
        MAX(id) as id,
        GROUP_CONCAT(DISTINCT uid ORDER BY id DESC) as uid_list,
        COUNT(*) as groupCount,
        activity,
        postid
    FROM user_activities a
    GROUP BY
        activity, postid
    ) a
    INNER JOIN user_activities b ON a.id = b.id
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