如何在MYSQL中解析一组前N条记录的查询结果
我有下面的查询,它给出了按用户id按desc顺序分组的名称计数。到目前为止,我已经做到了,但不能超过这一步。我想在每个用户的前2个记录的名称列中添加一个 目前的查询是:如何在MYSQL中解析一组前N条记录的查询结果,mysql,sql,ruby-on-rails-3,ruby-on-rails-4,Mysql,Sql,Ruby On Rails 3,Ruby On Rails 4,我有下面的查询,它给出了按用户id按desc顺序分组的名称计数。到目前为止,我已经做到了,但不能超过这一步。我想在每个用户的前2个记录的名称列中添加一个 目前的查询是: SELECT t.*, IF(@grp = t.user_id, @rowno := @rowno + 1, @rowno := 1) AS rowno, @grp := t.user_id AS u_id FROM (SELECT notes.user_id,
SELECT t.*,
IF(@grp = t.user_id, @rowno := @rowno + 1, @rowno := 1) AS rowno,
@grp := t.user_id AS u_id
FROM (SELECT notes.user_id,
t.name name,
Count(t.name) ct
FROM notes
INNER JOIN tags t
ON notes.id = t.note_id
GROUP BY notes.user_id,
t.name
ORDER BY notes.user_id,
Count(t.name) DESC) t;
它给出了以下结果:
+---------+------------+----+-------+-----+
| user_id | name | ct | rowno | uid |
+---------+------------+----+-------+-----+
| 282 | realifex | 1 | 1 | 282 |
+---------+------------+----+-------+-----+
| 282 | clear | 1 | 2 | 282 |
+---------+------------+----+-------+-----+
| 282 | thinking | 1 | 3 | 282 |
+---------+------------+----+-------+-----+
| 282 | refreshing | 1 | 4 | 282 |
+---------+------------+----+-------+-----+
| 285 | solid | 2 | 1 | 285 |
+---------+------------+----+-------+-----+
| 285 | clear | 1 | 2 | 285 |
+---------+------------+----+-------+-----+
| 285 | thinking | 1 | 3 | 285 |
+---------+------------+----+-------+-----+
| 287 | holidays | 3 | 1 | 287 |
+---------+------------+----+-------+-----+
| 287 | Larry | 3 | 2 | 287 |
+---------+------------+----+-------+-----+
| 287 | travel | 2 | 3 | 287 |
+---------+------------+----+-------+-----+
| 287 | thinking | 1 | 4 | 287 |
+---------+------------+----+-------+-----+
我试图将每个用户组的前2个结果合并到一列中,如下所示:
+---------+----------------+
| user_id | name |
+---------+----------------+
| 282 | realifex,clear |
+---------+----------------+
| 285 | solid, clear |
+---------+----------------+
| 287 | Larry,travel |
+---------+----------------+
Ue group_concat:
注:
@rn和@grp的表达式是单个表达式。MySQL不保证SELECT中表达式的求值顺序,因此单个表达式是安全分配这两个变量的唯一方法。
变量已初始化。
WHERE子句是确定前2名的地方。
嘿@Gordon谢谢你的回答,但我面临语法问题。试图解决它,但没有运气。面临以下错误。您的SQL语法有错误;查看与您的MySQL服务器版本对应的手册,了解使用near的正确语法IF@grp:=t.user_id,1,1'在第行4@Prem . . . 在前一行中有一个关于if的额外参数。非常感谢您的努力和帮助,但我对查询进行了一些调整,使其运行并且正在运行,但结果不一样。查询结果没有连接,每个组只有一个名称,而不是前两个结果282 | realifex | | 285 | solid | | 287 | Larry |谢谢@Gordon我能够理解整个查询并得到结果。再次感谢你。
SELECT group_id, group_concat(name order by rn) as names
FROM (SELECT t.*,
(@rn := IF(@grp = t.user_id, @rowno := @rowno + 1,
IF(@grp := t.user_id, 1, 1)
)
) as rn
FROM (SELECT n.user_id, t.name, n.name, Count(t.name) ct
FROM notes n INNER JOIN
tags t
ON notes.id = t.note_id
GROUP BY n.user_id, t.name
ORDER BY n.user_id, Count(t.name) DESC
) t CROSS JOIN
(SELECT @rn := 0, @grp := -1) params
) t
WHERE rn <= 2
GROUP BY user_id;