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mysql分组排序如何取第一条数据

2023-07-20 17:01:39 作者：GoodStudyAndDayDayUp

这篇文章主要介绍了mysql分组排序如何取第一条数据问题，具有很好的参考价值，希望对大家有所帮助。如有错误或未考虑完全的地方，望不吝赐教

mysql分组排序取第一条数据

需求：

mysql 根据某一个字段分组，然后组内排序，最后每组取排序后的第一条数据

1. 先使用（分组字段+排序字段）排序

相当于实现了分组和排序，只是没有根据分组字段聚合，此时每个分组的第一条数据就是我们需要的目标数据。

2. 再按分组字段分组，取第一条即可

实例如下：

with 
t_picture as(
 SELECT npi_product_id,is_default_one,update_time, uri FROM datahub_product_attachment where type=1 ORDER BY npi_product_id,is_default_one DESC,update_time DESC
)
SELECT npi_product_id, (ARRAY_AGG(uri))[1] as uri FROM t_picture  group by npi_product_id

必须在分组前排序，分组后排序是对分组字段和聚合字段排序。

mysql分组求组内的最大最小值

可能有一段时间没写代码，今天在项目里发现了一个bug，记录下~

（1）数据准备

《节假日表》
CREATE TABLE `app_calendar_holiday` (
  `holiday_name` varchar(50) NOT NULL COMMENT '假期名',
  `holiday_date` varchar(10) NOT NULL COMMENT '假期的日期（yyyy-MM-dd）',
  `rel_date` varchar(10) NOT NULL COMMENT '节假日相关联的日子',
  `rel_date_status` int(1) NOT NULL COMMENT '节假日相关联的日是否上班（	1:放假,2:上班）',
  `is_delete` int(1) NOT NULL DEFAULT '0' COMMENT '删除flg',
  `create_time` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP COMMENT '创建时间',
  `update_time` datetime DEFAULT NULL ON UPDATE CURRENT_TIMESTAMP COMMENT '更新时间',
  UNIQUE KEY `rel_date` (`rel_date`) USING BTREE
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COMMENT='假期表';
-- ----------------------------
-- Records of app_calendar_holiday
-- ----------------------------
INSERT INTO `app_calendar_holiday` VALUES ('元旦', '2019-01-01', '2018-12-29', '2', '0', '2019-09-01 23:08:09', '2019-09-02 10:48:11');
INSERT INTO `app_calendar_holiday` VALUES ('元旦', '2019-01-01', '2018-12-30', '1', '0', '2019-09-01 23:08:10', '2019-09-02 10:48:16');
INSERT INTO `app_calendar_holiday` VALUES ('元旦', '2019-01-01', '2018-12-31', '1', '0', '2019-09-01 23:08:09', '2019-09-02 10:48:17');
INSERT INTO `app_calendar_holiday` VALUES ('元旦', '2019-01-01', '2019-01-01', '1', '0', '2019-09-01 23:08:10', '2019-09-02 10:48:18');
INSERT INTO `app_calendar_holiday` VALUES ('春节', '2019-02-05', '2019-02-02', '2', '0', '2019-09-01 23:08:11', '2019-09-02 10:48:22');
INSERT INTO `app_calendar_holiday` VALUES ('春节', '2019-02-05', '2019-02-03', '2', '0', '2019-09-01 23:08:11', '2019-09-02 10:48:23');
INSERT INTO `app_calendar_holiday` VALUES ('春节', '2019-02-05', '2019-02-04', '1', '0', '2019-09-01 23:08:11', '2019-09-02 10:48:24');
INSERT INTO `app_calendar_holiday` VALUES ('春节', '2019-02-05', '2019-02-05', '1', '0', '2019-09-01 23:08:11', '2019-09-02 10:48:25');
INSERT INTO `app_calendar_holiday` VALUES ('春节', '2019-02-05', '2019-02-06', '1', '0', '2019-09-01 23:08:11', '2019-09-02 10:48:25');
INSERT INTO `app_calendar_holiday` VALUES ('春节', '2019-02-05', '2019-02-07', '1', '0', '2019-09-01 23:08:11', '2019-09-02 10:48:26');
INSERT INTO `app_calendar_holiday` VALUES ('春节', '2019-02-05', '2019-02-08', '1', '0', '2019-09-01 23:08:11', '2019-09-02 10:48:26');
INSERT INTO `app_calendar_holiday` VALUES ('春节', '2019-02-05', '2019-02-09', '1', '0', '2019-09-01 23:08:11', '2019-09-02 10:48:27');
INSERT INTO `app_calendar_holiday` VALUES ('春节', '2019-02-05', '2019-02-10', '1', '0', '2019-09-01 23:08:11', '2019-09-02 10:48:27');
INSERT INTO `app_calendar_holiday` VALUES ('清明节', '2019-04-05', '2019-04-05', '1', '0', '2019-09-01 23:08:12', '2019-09-02 10:59:26');
INSERT INTO `app_calendar_holiday` VALUES ('清明节', '2019-04-05', '2019-04-06', '1', '0', '2019-09-01 23:08:12', '2019-09-02 10:59:28');
INSERT INTO `app_calendar_holiday` VALUES ('清明节', '2019-04-05', '2019-04-07', '1', '0', '2019-09-01 23:08:13', '2019-09-02 10:59:30');
INSERT INTO `app_calendar_holiday` VALUES ('劳动节', '2019-05-01', '2019-04-28', '2', '0', '2019-09-01 23:08:14', '2019-09-02 10:48:31');
INSERT INTO `app_calendar_holiday` VALUES ('劳动节', '2019-05-01', '2019-05-01', '1', '0', '2019-09-01 23:08:13', '2019-09-02 10:48:45');
INSERT INTO `app_calendar_holiday` VALUES ('劳动节', '2019-05-01', '2019-05-02', '1', '0', '2019-09-01 23:08:13', '2019-09-02 10:48:46');
INSERT INTO `app_calendar_holiday` VALUES ('劳动节', '2019-05-01', '2019-05-03', '1', '0', '2019-09-01 23:08:14', '2019-09-02 10:48:47');
INSERT INTO `app_calendar_holiday` VALUES ('劳动节', '2019-05-01', '2019-05-04', '1', '0', '2019-09-01 23:08:14', '2019-09-02 10:48:47');
INSERT INTO `app_calendar_holiday` VALUES ('劳动节', '2019-05-01', '2019-05-05', '2', '0', '2019-09-01 23:08:14', '2019-09-02 10:48:48');
INSERT INTO `app_calendar_holiday` VALUES ('端午节', '2019-06-07', '2019-06-07', '1', '0', '2019-09-01 23:08:14', '2019-09-02 10:48:53');
INSERT INTO `app_calendar_holiday` VALUES ('端午节', '2019-06-07', '2019-06-08', '1', '0', '2019-09-01 23:08:14', '2019-09-02 10:48:54');
INSERT INTO `app_calendar_holiday` VALUES ('端午节', '2019-06-07', '2019-06-09', '1', '0', '2019-09-01 23:08:14', '2019-09-02 10:48:55');
INSERT INTO `app_calendar_holiday` VALUES ('中秋节', '2019-09-13', '2019-09-13', '1', '0', '2019-09-01 23:08:16', '2019-09-02 10:48:59');
INSERT INTO `app_calendar_holiday` VALUES ('中秋节', '2019-09-13', '2019-09-14', '1', '0', '2019-09-01 23:08:16', '2019-09-02 10:49:00');
INSERT INTO `app_calendar_holiday` VALUES ('中秋节', '2019-09-13', '2019-09-15', '1', '0', '2019-09-01 23:08:16', '2019-09-02 10:49:01');
INSERT INTO `app_calendar_holiday` VALUES ('国庆节', '2019-10-01', '2019-09-29', '2', '0', '2019-09-01 23:08:17', '2019-09-02 10:49:04');
INSERT INTO `app_calendar_holiday` VALUES ('国庆节', '2019-10-01', '2019-10-01', '1', '0', '2019-09-01 23:08:17', '2019-09-02 10:49:05');
INSERT INTO `app_calendar_holiday` VALUES ('国庆节', '2019-10-01', '2019-10-02', '1', '0', '2019-09-01 23:08:17', '2019-09-02 10:49:06');
INSERT INTO `app_calendar_holiday` VALUES ('国庆节', '2019-10-01', '2019-10-03', '1', '0', '2019-09-01 23:08:17', '2019-09-02 10:49:06');
INSERT INTO `app_calendar_holiday` VALUES ('国庆节', '2019-10-01', '2019-10-04', '1', '0', '2019-09-01 23:08:17', '2019-09-02 10:49:06');
INSERT INTO `app_calendar_holiday` VALUES ('国庆节', '2019-10-01', '2019-10-05', '1', '0', '2019-09-01 23:08:17', '2019-09-02 10:49:07');
INSERT INTO `app_calendar_holiday` VALUES ('国庆节', '2019-10-01', '2019-10-06', '1', '0', '2019-09-01 23:08:17', '2019-09-02 10:49:08');
INSERT INTO `app_calendar_holiday` VALUES ('国庆节', '2019-10-01', '2019-10-07', '1', '0', '2019-09-01 23:08:17', '2019-09-02 10:49:10');
INSERT INTO `app_calendar_holiday` VALUES ('国庆节', '2019-10-01', '2019-10-12', '2', '0', '2019-09-01 23:08:17', '2019-09-02 10:49:11');

（2）需求明确

查询条件：某年某月 yyyy-MM

查询结果：求出在该月里的节假日

例子：条件为2019-09，返回中秋节的2019-09-13 ~ 2019-09-15 ，国庆节的放假日2019-10-1~2019-10-7 。

并输出对应的节假日日期、节假日名。

（3）错误log

Expression #2 of SELECT list is not in GROUP BY clause and contains nonaggregated column 'panshi.t1.holiday_name' which is not functionally dependent on columns in GROUP BY clause; this is incompatible with sql_mode=only_full_group_by

提示的 panshi.t1.holiday_name 无法取出。

（4）错误sql

SELECT
		t1.holiday_date AS holidayDate,
		t1.holiday_name AS holidayName,
		MIN(t1.rel_date) AS minRelDate,
		MAX(t1.rel_date) AS maxRelDate
	FROM
		app_calendar_holiday t1
	INNER JOIN (
		SELECT DISTINCT
			holiday_date
		FROM
			`app_calendar_holiday`
		WHERE
			LEFT (rel_date, 7) = '2019-09'
	) t2 ON t1.holiday_date = t2.holiday_date
	WHERE
		t1.rel_date_status = 1
	GROUP BY
		t1.holiday_date;

（5）纠正后的SQL

纠正：select 的字段要是group by 所允许的！！！追加分组的字段 t1.holiday_date

方法一：分组 + 每组里使用聚合函数

SELECT
		t1.holiday_date AS holidayDate,
		t1.holiday_name AS holidayName,
		MIN(t1.rel_date) AS minRelDate,
		MAX(t1.rel_date) AS maxRelDate
	FROM
		app_calendar_holiday t1
	INNER JOIN (
		SELECT DISTINCT
			holiday_date
		FROM
			`app_calendar_holiday`
		WHERE
			LEFT (rel_date, 7) = '2019-09'
	) t2 ON t1.holiday_date = t2.holiday_date
	WHERE
		t1.rel_date_status = 1
	GROUP BY
		t1.holiday_date,
		t1.holiday_name;

方法二：分组 + 每组里日期排序，再取第一个

SELECT
		t1.holiday_date AS holidayDate,
		t1.holiday_name AS holidayName,
		SUBSTRING_INDEX(
			GROUP_CONCAT(
				t1.rel_date
				ORDER BY
					t1.rel_date ASC
			),
			',',
			1
		) AS minRelDate,
		SUBSTRING_INDEX(
			GROUP_CONCAT(
				t1.rel_date
				ORDER BY
					t1.rel_date DESC
			),
			',',
			1
		) AS maxRelDate
	FROM
		app_calendar_holiday t1
	INNER JOIN (
		SELECT DISTINCT
			holiday_date
		FROM
			`app_calendar_holiday`
		WHERE
			LEFT (rel_date, 7) = '2019-09'
	) t2 ON t1.holiday_date = t2.holiday_date
	WHERE
		t1.rel_date_status = 1
	GROUP BY
		t1.holiday_date,
		t1.holiday_name;

结果：都是

在这里插入图片描述

（6）拓展和总结

两者方法都需要注意，如果SELECT （某些字段） FROM xxxx 。。。，SELECT 后的字段必须是group by 后面的，或者使用聚合函数。

我出错就在于，之前的sql 里 GROPY BY 只是写了节假日期，但又需要取出节假日名。

方法一：

注意，再mysql 里用到group_concat的时候，拼接后的字符串是有长度限制的。默认是1024,可以通过修改mysql配置文件里的【group_concat_max_len】字段

其实这种情况使用 group_concat + order by 的组合，有点多余的，因为已经有聚合函数的出现。

不过想想，如果分组后是组内需要按照某些字段排序的，返回字符串类型的，可以用这个方法

总结

以上为个人经验，希望能给大家一个参考，也希望大家多多支持脚本之家。