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Mysql / Select / MAX() / GROUP BY

[英]Mysql / Select / MAX() / GROUP BY

 原文  2014-04-10 10:35:34  5   3    mysql/ select/ join/ group-by/ max

问题描述

Here the structure of the database (reduced):这里的数据库结构（缩减）：

CREATE TABLE IF NOT EXISTS `TK_servers` (
  `id` int(11),
  `server_id` varchar(11) ,
  `worker_id` varchar(20) ,
  `date_ins` datetime ,
  `avg` varchar(10)
) ENGINE=MyISAM  DEFAULT CHARSET=latin1  ;

INSERT INTO `TK_servers` (`id`, `server_id`, `worker_id`, `date_ins`, `avg`)
VALUES
(108253, 12, 'srva', '2014-04-10 12:00:31', ''),
(108250, 31, 'srva', '2014-04-10 12:00:31', '2.337'),
(108249, 19, 'srva', '2014-04-10 12:00:31', '5.883'),
(108248, 10, 'srva', '2014-04-10 12:00:31', '8.813'),
(108223, 12, 'srvb', '2014-04-10 12:00:22', ''),
(108220, 31, 'srvb', '2014-04-10 12:00:22', '31.183'),
(108219, 19, 'srvb', '2014-04-10 12:00:22', '34.412'),
(108218, 10, 'srvb', '2014-04-10 12:00:22', '36.724'),
(108193, 12, 'srva', '2014-04-10 11:55:31', ''),
(108190, 31, 'srva', '2014-04-10 11:55:31', '2.500'),
(108189, 19, 'srva', '2014-04-10 11:55:31', '5.835'),
(108188, 10, 'srva', '2014-04-10 11:55:31', '8.883'),
(108163, 12, 'srvb', '2014-04-10 11:55:23', ''),
(108160, 31, 'srvb', '2014-04-10 11:55:23', '30.766'),
(108159, 19, 'srvb', '2014-04-10 11:55:23', '42.801'),
(108158, 10, 'srvb', '2014-04-10 11:55:23', '37.093'),
(108133, 12, 'srva', '2014-04-10 11:50:31', ''),
(108130, 31, 'srva', '2014-04-10 11:50:31', '2.538'),
(108129, 19, 'srva', '2014-04-10 11:50:31', '5.397'),
(108128, 10, 'srva', '2014-04-10 11:50:31', '8.737'),
(108103, 12, 'srvb', '2014-04-10 11:50:22', ''),
(108099, 31, 'srvb', '2014-04-10 11:50:22', '30.948'),
(108098, 19, 'srvb', '2014-04-10 11:50:22', '34.279'),
(108097, 10, 'srvb', '2014-04-10 11:50:22', '36.418'),
(108073, 12, 'srva', '2014-04-10 11:45:32', ''),
(108070, 31, 'srva', '2014-04-10 11:45:32', '2.502'),
(108069, 19, 'srva', '2014-04-10 11:45:32', '5.568'),
(108068, 10, 'srva', '2014-04-10 11:45:32', '9.202'),
(108043, 12, 'srvb', '2014-04-10 11:45:22', ''),
(108041, 19, 'srvb', '2014-04-10 11:45:22', '46.626'),
(108039, 31, 'srvb', '2014-04-10 11:45:22', '30.827'),
(108038, 10, 'srvb', '2014-04-10 11:45:22', '37.197'),
(108013, 12, 'srva', '2014-04-10 11:40:32', ''),
(108010, 31, 'srva', '2014-04-10 11:40:32', '2.604'),
(108009, 19, 'srva', '2014-04-10 11:40:32', '5.252'),
(108008, 10, 'srva', '2014-04-10 11:40:32', '8.816'),
(107983, 12, 'srvb', '2014-04-10 11:40:22', ''),
(107980, 31, 'srvb', '2014-04-10 11:40:22', '31.632'),
(107979, 19, 'srvb', '2014-04-10 11:40:22', '43.913'),
(107978, 10, 'srvb', '2014-04-10 11:40:22', '36.796'),
(107953, 12, 'srva', '2014-04-10 11:35:32', ''),
(107950, 31, 'srva', '2014-04-10 11:35:32', '2.369'),
(107949, 19, 'srva', '2014-04-10 11:35:32', '5.876'),
(107948, 10, 'srva', '2014-04-10 11:35:32', '8.721'),
(107923, 12, 'srvb', '2014-04-10 11:35:23', ''),
(107920, 31, 'srvb', '2014-04-10 11:35:23', '31.595'),
(107919, 19, 'srvb', '2014-04-10 11:35:23', '45.858'),
(107918, 10, 'srvb', '2014-04-10 11:35:23', '36.661'),
(107893, 12, 'srva', '2014-04-10 11:30:31', ''),
(107890, 31, 'srva', '2014-04-10 11:30:31', '2.508'),
(107889, 19, 'srva', '2014-04-10 11:30:31', '6.308'),
(107888, 10, 'srva', '2014-04-10 11:30:31', '38.151'),
(107863, 12, 'srvb', '2014-04-10 11:30:23', ''),
(107860, 31, 'srvb', '2014-04-10 11:30:23', '31.162'),
(107859, 19, 'srvb', '2014-04-10 11:30:23', '34.515'),
(107858, 10, 'srvb', '2014-04-10 11:30:23', '36.720'),
(107833, 12, 'srva', '2014-04-10 11:25:31', ''),
(107830, 31, 'srva', '2014-04-10 11:25:31', '2.722'),
(107829, 19, 'srva', '2014-04-10 11:25:31', '5.965'),
(107828, 10, 'srva', '2014-04-10 11:25:31', '8.642'),
(107803, 12, 'srvb', '2014-04-10 11:25:23', ''),
(107799, 31, 'srvb', '2014-04-10 11:25:23', '31.525'),
(107798, 19, 'srvb', '2014-04-10 11:25:23', '34.465'),
(107797, 10, 'srvb', '2014-04-10 11:25:23', '36.893'),
(107773, 12, 'srva', '2014-04-10 11:20:30', ''),
(107770, 31, 'srva', '2014-04-10 11:20:30', '2.373'),
(107769, 19, 'srva', '2014-04-10 11:20:30', '5.206'),
(107768, 10, 'srva', '2014-04-10 11:20:30', '8.749'),
(107743, 12, 'srvb', '2014-04-10 11:20:23', ''),
(107740, 31, 'srvb', '2014-04-10 11:20:23', '31.053'),
(107739, 19, 'srvb', '2014-04-10 11:20:23', '35.096'),
(107738, 10, 'srvb', '2014-04-10 11:20:23', '36.680'),
(107713, 12, 'srva', '2014-04-10 11:15:31', ''),
(107710, 31, 'srva', '2014-04-10 11:15:31', '2.489'),
(107709, 19, 'srva', '2014-04-10 11:15:31', '6.519'),
(107708, 10, 'srva', '2014-04-10 11:15:31', '15.279'),
(107683, 12, 'srvb', '2014-04-10 11:15:23', ''),
(107680, 31, 'srvb', '2014-04-10 11:15:23', '31.236'),
(107679, 19, 'srvb', '2014-04-10 11:15:23', '34.834'),
(107678, 10, 'srvb', '2014-04-10 11:15:23', '37.294'),
(107653, 12, 'srva', '2014-04-10 11:10:31', ''),
(107650, 31, 'srva', '2014-04-10 11:10:31', '2.561'),
(107649, 19, 'srva', '2014-04-10 11:10:31', '5.446'),
(107648, 10, 'srva', '2014-04-10 11:10:31', '8.763'),
(107623, 12, 'srvb', '2014-04-10 11:10:22', ''),
(107620, 31, 'srvb', '2014-04-10 11:10:22', '30.716'),
(107619, 19, 'srvb', '2014-04-10 11:10:22', '34.679'),
(107618, 10, 'srvb', '2014-04-10 11:10:22', '36.854'),
(107593, 12, 'srva', '2014-04-10 11:05:32', ''),
(107590, 31, 'srva', '2014-04-10 11:05:32', '2.355'),
(107589, 19, 'srva', '2014-04-10 11:05:32', '5.720'),
(107588, 10, 'srva', '2014-04-10 11:05:32', '10.779'),
(107563, 12, 'srvb', '2014-04-10 11:05:22', ''),
(107560, 31, 'srvb', '2014-04-10 11:05:22', '31.217'),
(107559, 19, 'srvb', '2014-04-10 11:05:22', '35.360'),
(107558, 10, 'srvb', '2014-04-10 11:05:22', '37.079'),
(107533, 12, 'srva', '2014-04-10 11:00:32', ''),
(107530, 31, 'srva', '2014-04-10 11:00:32', '2.526'),
(107529, 19, 'srva', '2014-04-10 11:00:32', '5.949'),
(107528, 10, 'srva', '2014-04-10 11:00:32', '8.691');

I want to list the MAX (avg) corresponding to worker_id.我想列出worker_id对应的MAX（平均）。

SELECT * FROM  `TK_servers`
JOIN (SELECT max(`avg`), (`id`) id FROM `TK_servers`
 WHERE `server_id` = '31'
 GROUP BY LEFT(date_ins,16) )
t2 ON t2.id = `TK_servers`.`id`

Result :结果 ：

ID     SERVER_ID  WORKER_ID   DATE_INS                        AVG     MAX(`AVG`)
108250    31      srva        April, 10 2014 12:00:31+0000    2.337   31.183 
108190    31      srva        April, 10 2014 11:55:31+0000    2.500   30.766 
108130    31      srva        April, 10 2014 11:50:31+0000    2.538   30.948 
108070    31      srva        April, 10 2014 11:45:32+0000    2.502   30.827 
......

error the max(avg) is worker_id srvb错误 max(avg) 是 worker_id srvb

3 个解决方案

解决方案1
 0  2014-04-10 10:42:32

Compare and contrast...比较和对比...

SELECT * FROM tk_servers ORDER BY avg DESC LIMIT 1;
+--------+-----------+-----------+---------------------+-------+
| id     | server_id | worker_id | date_ins            | avg   |
+--------+-----------+-----------+---------------------+-------+
| 108068 | 10        | srva      | 2014-04-10 11:45:32 | 9.202 |
+--------+-----------+-----------+---------------------+-------+

SELECT * FROM tk_servers ORDER BY avg+0 DESC LIMIT 1;
+--------+-----------+-----------+---------------------+--------+
| id     | server_id | worker_id | date_ins            | avg    |
+--------+-----------+-----------+---------------------+--------+
| 108041 | 19        | srvb      | 2014-04-10 11:45:22 | 46.626 |
+--------+-----------+-----------+---------------------+--------+

So, hopefully this underlines the importance of using the correct data types.因此，希望这强调了使用正确数据类型的重要性。 In this case, it should be DECIMAL(6,3) NULL, not VARCHAR!在这种情况下，它应该是 DECIMAL(6,3) NULL，而不是 VARCHAR！

解决方案2
 0  2014-04-10 10:44:52

the problem is your avgerage column is in varchar you should must change.问题是您的平均列在varchar您必须更改。

and then use the code like:然后使用如下代码：

select id, server_id, worker_id, date_ins ,max(avg) from tk_servers

http://sqlfiddle.com/#!2/4d3529/32 http://sqlfiddle.com/#!2/4d3529/32

UPDATE:1更新：1

SELECT * 
FROM  `TK_servers`
JOIN 
(
SELECT 
  max(`avg`), 
      (`id`) id 
  FROM `TK_servers`
  WHERE `server_id` = '31'
  GROUP BY LEFT(date_ins,16) 
)t2 
ON t2.id = `TK_servers`.`id`
LIMIT 1;

http://sqlfiddle.com/#!2/4d3529/35 http://sqlfiddle.com/#!2/4d3529/35

解决方案3
 0  2014-04-10 11:10:27

Change the data type of AVG field from varchar to double and then try to fetch the MAX(AVG) it will work.将 AVG 字段的数据类型从 varchar 更改为 double，然后尝试获取 MAX(AVG) 它将起作用。

Hope the avg is making the problem希望平均值是问题所在

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