Mysql 按列对项目进行分组，并按其他列排序

我有下表，我想为客户进行最新评级 基本上，每当用户更新评级时，计数将增加，并在表中创建一个条目。下表如下

-----------------------------------------------------
|_id| name   | client_id | user_id | rating | count |
-----------------------------------------------------
|1  | Four   |   1       |    1    |   4    |   1   |
|2  | three  |   1       |    1    |   3    |   2   |
|3  | two    |   1       |    1    |   2    |   3   |
|4  | five   |   1       |    1    |   5    |   4   |
|5  | two    |   1       |    2    |   2    |   1   |
|6  | three  |   1       |    2    |   3    |   2   |
|7  | two    |   2       |    1    |   2    |   1   |
|8  | three  |   2       |    1    |   3    |   2   |
-----------------------------------------------------

对于

客户id 1的评级

我希望

-----------------------------------------------------
|_id| name   | client_id | user_id | rating | count |
-----------------------------------------------------
|4  | five   |   1       |    1    |   5    |   4   |
|6  | three  |   1       |    2    |   3    |   2   |
-----------------------------------------------------

到目前为止，我尝试了

SELECT*fromtest
其中client_id=1按client_id分组按count desc排序
但是没有得到预期的结果，有什么帮助吗？？？
您可以尝试以下方法

select _id, name, client_id, user_id, rating, max(count)
from clients 
group by client_id

试试看

您可以在与相同的表上使用
left join

select t1.* from test t1 
left join test t2 on t1.user_id = t2.user_id 
and t1.client_id = t2.client_id 
and t1._id < t2._id 
where 
t2._id is null 
and t1.client_id = 1 
order by t1.`count` desc;

更新：从注释如何将另一个表连接到上面，这里是一个示例

mysql> select * from users ;
+------+------+
| _id  | name |
+------+------+
|    1 | AAA  |
|    2 | BBB  |
+------+------+
2 rows in set (0.00 sec)

mysql> select * from test ;
+------+-------+-----------+---------+--------+-------+
| _id  | name  | client_id | user_id | rating | count |
+------+-------+-----------+---------+--------+-------+
|    1 | four  |         1 |       1 |      4 |     1 |
|    2 | three |         1 |       1 |      3 |     2 |
|    3 | two   |         1 |       1 |      2 |     3 |
|    4 | five  |         1 |       1 |      5 |     4 |
|    5 | two   |         1 |       2 |      2 |     1 |
|    6 | three |         1 |       2 |      3 |     2 |
|    7 | two   |         2 |       1 |      2 |     1 |
|    8 | three |         2 |       1 |      3 |     2 |
+------+-------+-----------+---------+--------+-------+

select t1.*,u.name from test t1 
join users u on u._id = t1.user_id
left join test t2 on t1.user_id = t2.user_id 
and t1.client_id = t2.client_id 
and t1._id < t2._id 
where 
t2._id is null 
and t1.client_id = 1 
order by t1.`count` desc;

请注意，
users
表的连接是内部连接，这将要求在
test
表中的
users
表中预设所有用户

如果
users
表中缺少一些用户，则使用
left join
这将为从
users
表中选择的数据提供空值。
为什么
\u id=5
不应出现在结果中？因为其与用户\u id 2相关的计数为1，所以_id6因为它的计数是2，这是客户端的最大值_id1我尝试了这个没有用，我在问题中也提到了谢谢，我得到了预期的结果，还有其他简单的查询吗？这些是最简单的：）强烈推荐，我想使用user_id从用户表中获取用户信息。我如何使用您的查询来实现这一点，基本上用户是另一个表。只需向用户表添加一个联接，然后选择要从用户表中选择的字段。如果表名是
users
，那么在第一种情况下，它将在第一次左键联接之前作为
join users u on u.user_id=t1.user_id
，在第二种情况下，在
联接（…）
之前它将是相同的，我正在尝试这样选择t1.*，u.*从测试t1在u上连接用户u。_id=t1.user\u id在t1上左连接测试t2.user\u id=t2.user\u id和t1.client\u id=t2.client\u id和t1。_idcount

desc；但是没有得到预期的结果

select t1.* from test t1 
join ( 
  select max(_id) as _id,
  client_id,
  user_id 
  from test 
  where client_id = 1 
  group by client_id,user_id 
)t2 
on t1._id = t2._id 
and t1.client_id = t2.client_id 
order by t1.`count` desc; 

mysql> select * from users ;
+------+------+
| _id  | name |
+------+------+
|    1 | AAA  |
|    2 | BBB  |
+------+------+
2 rows in set (0.00 sec)

mysql> select * from test ;
+------+-------+-----------+---------+--------+-------+
| _id  | name  | client_id | user_id | rating | count |
+------+-------+-----------+---------+--------+-------+
|    1 | four  |         1 |       1 |      4 |     1 |
|    2 | three |         1 |       1 |      3 |     2 |
|    3 | two   |         1 |       1 |      2 |     3 |
|    4 | five  |         1 |       1 |      5 |     4 |
|    5 | two   |         1 |       2 |      2 |     1 |
|    6 | three |         1 |       2 |      3 |     2 |
|    7 | two   |         2 |       1 |      2 |     1 |
|    8 | three |         2 |       1 |      3 |     2 |
+------+-------+-----------+---------+--------+-------+

select t1.*,u.name from test t1 
join users u on u._id = t1.user_id
left join test t2 on t1.user_id = t2.user_id 
and t1.client_id = t2.client_id 
and t1._id < t2._id 
where 
t2._id is null 
and t1.client_id = 1 
order by t1.`count` desc;

+------+-------+-----------+---------+--------+-------+------+
| _id  | name  | client_id | user_id | rating | count | name |
+------+-------+-----------+---------+--------+-------+------+
|    4 | five  |         1 |       1 |      5 |     4 | AAA  |
|    6 | three |         1 |       2 |      3 |     2 | BBB  |
+------+-------+-----------+---------+--------+-------+------+