mysql中GROUP_CONCAT函数使用及遇到问题详解

概要

` group_concat函数是mysql中非常实用的函数，它可以将同一个分组下的行拼接在一起。其完整语法：GROUP_CONCAT([DISTINCT] 要连接的字段 [Order BY ASC/DESC 排序字段] [Separator ‘分隔符’])

使用技巧

1. 建表、插入数据

#建表语句
CREATE TABLE `test_group_concat` (
  `id` int(11) NOT NULL COMMENT 'id',
  `age` int(11) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;
#插入测试数据
INSERT INTO `test`.`test_group_concat` (`id`, `age`) VALUES (1, 20);
INSERT INTO `test`.`test_group_concat` (`id`, `age`) VALUES (1, 20);
INSERT INTO `test`.`test_group_concat` (`id`, `age`) VALUES (1, 10);
INSERT INTO `test`.`test_group_concat` (`id`, `age`) VALUES (3, 30);
INSERT INTO `test`.`test_group_concat` (`id`, `age`) VALUES (3, 40);
INSERT INTO `test`.`test_group_concat` (`id`, `age`) VALUES (3, 40);
INSERT INTO `test`.`test_group_concat` (`id`, `age`) VALUES (4, 50);
INSERT INTO `test`.`test_group_concat` (`id`, `age`) VALUES (4, 60);
#基本查询
SELECT * FROM test_group_concat

2.以id分组，把age字段的值拼成一行，逗号分隔(默认)

select id,group_concat(age) from test_group_concat group by id;

3.以id分组，把age字段的值拼成 一行，分号分隔

select id,group_concat(age separator ';') from test_group_concat group by id;

4.以id分组，把去冗余的age字段的值打印在一行

select id,group_concat(distinct age) from test_group_concat group by id;

5.以id分组，把age字段的值打印在一行，逗号分隔，以age排倒序

select id,group_concat(age order by age desc) from test_group_concat group by id; 

发现问题

在项目用到如下sql

SELECT
	GROUP_CONCAT( c.goods_detail_id ) 
FROM
	air_out_order a
	LEFT JOIN air_out_order_detail b ON b.order_id = a.id
	LEFT JOIN air_out_good_record c ON c.order_detail_id = b.id; 

查询结果：

713278402284617792,722329309878140931,722329309878140949,722329309878140973,722329309878140939,715342356376936480,715342356376936482,715342356381130806,715342356376936484,715342356381130810,713278240841662516,713278240841662476,713278240841662520,715342356381130876,715342356381130940,715342356385325066,715342356385325132,715342356385325196,715342356385325260,715342356376936526,715342356381130812,715342356381130890,715342356381130964,744788201669005316,744788201669005380,744788201673199622,744788201669005330,744788201669005394,744788201752891404,744788201664811012,744788201669005344,744788201669005408,744788201752891418,744788201669005338,744788201669005410,744788201664811016,744788201669005354,744788201669005424,744788201664811030,744788201669005368,744788201673199616,744788201752891400,744788201669005312,745061736895352916,745061736891158544,745061736895352852,745061736895352930,745061736891158558,745061736895352866,745061736895352944,745061736891158572,745061736895352880,745061736895352958,74506173689115858

而实际上

SELECT
c.goods_detail_id
FROM
	air_out_order a
	LEFT JOIN air_out_order_detail b ON b.order_id = a.id
	LEFT JOIN air_out_good_record c ON c.order_detail_id = b.id;

的查询结果为：

713278402284617792
722329309878140931,722329309878140949,722329309878140973,722329309878140939
715342356376936480
715342356376936482
715342356381130806
715342356376936484
715342356381130810
713278240841662516
713278240841662476
713278240841662520
715342356381130876,715342356381130940,715342356385325066,715342356385325132,715342356385325196,715342356385325260,715342356376936526,715342356381130812,715342356381130890,715342356381130964
744788201669005316,744788201669005380,744788201673199622,744788201669005330,744788201669005394,744788201752891404,744788201664811012,744788201669005344,744788201669005408,744788201752891418
744788201669005338,744788201669005410,744788201664811016,744788201669005354,744788201669005424,744788201664811030,744788201669005368,744788201673199616,744788201752891400,744788201669005312
745061736895352916,745061736891158544,745061736895352852,745061736895352930,745061736891158558,745061736895352866,745061736895352944,745061736891158572,745061736895352880,745061736895352958,745061736891158586,745061736895352894,745061736891158536,745061736895352844,745061736895352908,745061736895352922,745061736891158550,745061736895352858,745061736895352936,745061736891158564,745061736895352872,745061736895352950,745061736891158578,745061736895352886,745061736895352964,745061736891158528,745061736895352836,745061736895352900,745061736895352914,745061736891158542
744788201669005318,744788201669005396,744788201669005334,744788201669005414,744788201669005352,744788201669005430,744788201664811022,744788201669005370,744788201752891394,744788201664811038
744788201664811020,744788201669005382,744788201752891416,744788201664811040,744788201669005400,744788201669005328,744788201669005420,744788201669005350,744788201673199618,744788201664811008
746171271546650637
746171271550844964
745061736895352842,745061736895352934,745061736895352862,745061736895352954,745061736891158548,745061736895352882,745061736891158568,745061736895352902,745061736895352832,745061736895352924
747357984740646912,747357984912613376,747357984782589952,747357984824532992,747357984652566528
747357984778395648
747357984753229824
745898989121159210,745898989108576268,745898989125353485,745898989116964869,745898989121159170,745898989121159184
745898989112770564,745898989121159168,745898989121159186,745898989121159202,745898989108576272,745898989125353481
745898989108576274,745898989116964877,745898989121159182,745898989121159206,745898989108576258,745898989116964865
745898989116964879
745898989112770562
745898989116964871,745898989121159180,745898989121159208,745898989108576260,745898989121159172,745898989121159194
745898989121159188,745898989125353477,745898989116964875,745898989121159198,745898989108576264,745898989121159178
747357984694509568,747357984904224768,747357984749035520,747357984807755776,747357984849698816,747357984644177920,747357984883253248,747357984715481088,747357984770007040,747357984828727296
747357984707092480,747357984795172864,747357984853893120,747357984895836160,747357984665149440,747357984736452608,747357984820338688,747357984866476032,747357984509960192,747357984916807680
745898989121159196
745898989121159200
762832940033040386
715342356385325082

要多得多，出现group_concat把数据给截断了，什么原因呢？

解决问题

由于group_concat有长度限制,默认1024个字符，所以解决的办法也就是将group_concat有长度限制设置足够大即可。

1）临时解决方案：

在命令行运行

SET SESSION group_concat_max_len = 18446744073709551615;
set global max_allowed_packet = 2*1024*1024*10;

2）永久解决方案：

首先找到mysql的配置文件，设置如下配置

max_allowed_packet = 20M
group_concat_max_len = 18446744073709551615

总结 

到此这篇关于mysql中GROUP_CONCAT函数使用及遇到问题的文章就介绍到这了,更多相关mysql GROUP_CONCAT函数内容请搜索脚本之家以前的文章或继续浏览下面的相关文章希望大家以后多多支持脚本之家！