在mysql中使用group by选择最小值

Posted 2023-05-09

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【中文标题】在mysql中使用group by选择最小值【英文标题】：Select minimum value with group by in mysql 【发布时间】：2013-03-26 05:12:19 【问题描述】：

我的数据库方案，

CREATE TABLE `result` (
`ID` bigint(21) NOT NULL AUTO_INCREMENT,
`datetime` datetime DEFAULT NULL,
`recordnum` int(11) DEFAULT NULL,
`recordtype` int(11) DEFAULT NULL,
`minvalue` int(11) DEFAULT NULL,
`maxvalue` int(11) DEFAULT NULL,
`data1` int(11) DEFAULT NULL,
`data2` int(11) DEFAULT NULL,
`area` varchar(32) DEFAULT NULL,
PRIMARY KEY (`ID`),
UNIQUE KEY `res` (`datetime`,`recordnum`,`area`)
) ENGINE=MyISAM AUTO_INCREMENT=7 DEFAULT CHARSET=latin1;

数据样本

INSERT INTO `result` VALUES ('1', '2013-03-26 12:03:31', '2', '1', '5', '10', '100', '200','Zone1');

INSERT INTO `result` VALUES ('2', '2013-03-26 12:03:31', '2', '1', '2', '7', '20', '20','Zone2');

INSERT INTO `result` VALUES ('3', '2013-03-26 12:03:31', '5', '2', '1', '2', '8', '15','Zone2');

INSERT INTO `result` VALUES ('4', '2013-03-26 12:00:31', '2', '1', '2', '7', '100', '200','Zone1');

INSERT INTO `result` VALUES ('5', '2013-03-26 12:00:31', '2', '1', '3', '9', '100', '200','Zone2');

INSERT INTO `result` VALUES ('6', '2013-03-26 12:00:31', '5', '2', '7', '2', '4', '10', 'Zone2');

INSERT INTO `result` VALUES ('7', '2013-03-25 12:03:31', '2', '1', '5', '10', '100', '200','Zone1');

INSERT INTO `result` VALUES ('8', '2013-03-25 12:03:31', '2', '1', '2', '7', '20', '20','Zone2');

INSERT INTO `result` VALUES ('9', '2013-03-25 12:03:31', '5', '2', '1', '2', '8', '15','Zone2');

INSERT INTO `result` VALUES ('10', '2013-03-25 12:00:31', '2', '1', '2', '7', '100', '200','Zone1');

INSERT INTO `result` VALUES ('11', '2013-03-25 12:00:31', '2', '1', '3', '9', '100', '200','Zone2');

INSERT INTO `result` VALUES ('12', '2013-03-25 12:00:31', '5', '2', '7', '2', '4', '10','Zone2');


INSERT INTO `result` VALUES ('13', '2013-03-25 11:03:31', '2', '1', '3', '10', '100','200', 'Zone1');

INSERT INTO `result` VALUES ('14', '2013-03-25 11:03:31', '2', '1', '8', '7', '20', '20','Zone2');

INSERT INTO `result` VALUES ('15', '2013-03-25 11:03:31', '5', '2', '2', '2', '8', '15','Zone2');

INSERT INTO `result` VALUES ('16', '2013-03-25 11:00:31', '2', '1', '1', '7', '100', '200','Zone1');

INSERT INTO `result` VALUES ('17', '2013-03-25 11:00:31', '2', '1', '9', '9', '100', '200','Zone2');

INSERT INTO `result` VALUES ('18', '2013-03-25 11:00:31', '5', '2', '12', '2', '4', '10','Zone2');

我想要的是在每个 recordnum 和 area 以及 date

的最小值为最小值时查询每个值

  +----+---------------------+-----------+-------+----------+----------+-------+-------+------------+
    | ID | datetime            | recordnum | area  |minvalue  | maxvalue | data1 | data2 | recordtype |
    +----+---------------------+-----------+-------+----------+----------+-------+-------+------------+
    |  2 | 2013-03-26 12:03:31 |         2 | Zone2 |        2 |        7 |    20 |    20 |          1 |
    |  3 | 2013-03-26 12:03:31 |         5 | Zone2 |        1 |        2 |     8 |    15 |          2 |
    |  4 | 2013-03-26 12:00:31 |         2 | Zone1 |        2 |        7 |   100 |   200 |          1 |
    |  8 | 2013-03-25 12:03:31 |         2 | Zone2 |        2 |        7 |    20 |    20 |          1 |
    |  9 | 2013-03-25 12:03:31 |         5 | Zone2 |        1 |        2 |     8 |    15 |          2 |
    | 16 | 2013-03-25 11:00:31 |         2 | Zone1 |        1 |        7 |   100 |   200 |          1 |
    +----+---------------------+-----------+-------+----------+----------+-------+-------+------------+

下面这个查询结果很好，但仍然显示重复记录，请帮助

SELECT  a.*
FROM    result a
        JOIN
        (
            SELECT  datetime as mindatetime,DATE(datetime) dateOnly,area, recordNum, MIN(minvalue) min_val
            FROM    result
            GROUP   BY dateOnly,area, recordNum
        ) b  ON a.area = b.area AND
                a.recordNUM = b.recordNum AND
                a.minvalue = b.min_val ;
+----+---------------------+-----------+------------+----------+----------+-------+-------+-------+
| ID | datetime            | recordnum | recordtype | minvalue | maxvalue | data1 | data2 | area  |
+----+---------------------+-----------+------------+----------+----------+-------+-------+-------+
|  2 | 2013-03-26 12:03:31 |         2 |          1 |        2 |        7 |    20 |    20 | Zone2 |
|  2 | 2013-03-26 12:03:31 |         2 |          1 |        2 |        7 |    20 |    20 | Zone2 |
|  3 | 2013-03-26 12:03:31 |         5 |          2 |        1 |        2 |     8 |    15 | Zone2 |
|  3 | 2013-03-26 12:03:31 |         5 |          2 |        1 |        2 |     8 |    15 | Zone2 |
|  4 | 2013-03-26 12:00:31 |         2 |          1 |        2 |        7 |   100 |   200 | Zone1 |
|  8 | 2013-03-25 12:03:31 |         2 |          1 |        2 |        7 |    20 |    20 | Zone2 |
|  8 | 2013-03-25 12:03:31 |         2 |          1 |        2 |        7 |    20 |    20 | Zone2 |
|  9 | 2013-03-25 12:03:31 |         5 |          2 |        1 |        2 |     8 |    15 | Zone2 |
|  9 | 2013-03-25 12:03:31 |         5 |          2 |        1 |        2 |     8 |    15 | Zone2 |
| 10 | 2013-03-25 12:00:31 |         2 |          1 |        2 |        7 |   100 |   200 | Zone1 |
| 16 | 2013-03-25 11:00:31 |         2 |          1 |        1 |        7 |   100 |   200 | Zone1 |
+----+---------------------+-----------+------------+----------+----------+-------+-------+-------+

【问题讨论】：

Get top n records for each group of grouped results 的可能重复项 【参考方案1】：

如何解决这个问题有很多变化。一种是使用单独的子查询，它为每个area and recordNum 获取最小值minvalue。然后将子查询的结果重新连接到原始表中，以便您可以获取行中的所有列。

SELECT  a.*
FROM    result a
        INNER JOIN
        (
            SELECT  area, recordNum, MIN(minvalue) min_val
            FROM    result
            GROUP   BY area, recordNum
        ) b  ON a.area = b.area AND
                a.recordNUM = b.recordNum AND
                a.minvalue = b.min_val

SQLFiddle Demo

输出

╔════╦══════════════════════════════╦═══════════╦════════════╦══════════╦══════════╦═══════╦═══════╦═══════╗
║ ID ║           DATETIME           ║ RECORDNUM ║ RECORDTYPE ║ MINVALUE ║ MAXVALUE ║ DATA1 ║ DATA2 ║ AREA  ║
╠════╬══════════════════════════════╬═══════════╬════════════╬══════════╬══════════╬═══════╬═══════╬═══════╣
║  2 ║ March, 26 2013 12:03:31+0000 ║         2 ║          1 ║        2 ║        7 ║    20 ║    20 ║ Zone2 ║
║  3 ║ March, 26 2013 12:03:31+0000 ║         5 ║          2 ║        1 ║        2 ║     8 ║    15 ║ Zone2 ║
║  4 ║ March, 26 2013 12:00:31+0000 ║         2 ║          1 ║        2 ║        7 ║   100 ║   200 ║ Zone1 ║
╚════╩══════════════════════════════╩═══════════╩════════════╩══════════╩══════════╩═══════╩═══════╩═══════╝

【讨论】：

谢谢，查询工作完美，我还有一个问题如何在一天添加组基数，我添加了group by DATE_FORMAT(DATETIME,'%Y-%m-%d') 所以我想要 MINVALUE 一天但它不起作用，谢谢 in adv。这里的结果缺少什么？你想格式化日期吗？为什么需要在 group by 子句中添加它？？不，查询结果有效，我想知道如何获取每日的最小值。我只是更新了顶部问题的数据样本，也是预期的结果，当 MINVALUE 记录最小时，只有 1 个基于组合 date 、 recordnum 和 area 的唯一记录。现在我得到了结果但仍然需要删除重复记录，有什么建议吗？

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