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MYSQL函数group_concat的使用 今天对一批数据要迁移转换，查了下，有group_concat这个函数简单实现字段的列转行设置，过程记录如下 一.测试数据准备mysql> use test;Database changedmysql> select * from t_kenyon;+------+| id |+------+| 1 || 123 || 789 || 345 || 78 |+------+5 rows in set (0.00 sec)二.使用经过 1.以默认的逗号作为分隔符mysql> select group_concat(id) from t_kenyon;+------------------+| group_concat(id) |+------------------+| 1,123,789,345,78 |+------------------+1 row in set (0.00 sec)2.对ID值进行排序后行转列mysql> select group_concat(id order by id) from t_kenyon;+------------------------------+| group_concat(id order by id) |+------------------------------+| 1,78,123,345,789 |+------------------------------+1 row in set (0.00 sec)3.使用其他分割符，如*和;等mysql> select group_concat(id separator '*') from t_kenyon;+--------------------------------+| group_concat(id separator '*') |+--------------------------------+| 1*123*789*345*78 |+--------------------------------+1 row in set (0.00 sec)
4.分隔符与排序结合起来用mysql> select group_concat(id order by id separator '_') from t_kenyon;+--------------------------------------------+| group_concat(id order by id separator '_') |+--------------------------------------------+| 1_78_123_345_789 |+--------------------------------------------+1 row in set (0.00 sec)5.对相同的值分组mysql> insert into t_kenyon values (78);Query OK, 1 row affected (0.00 sec) mysql> select group_concat(id) from t_kenyon group by id;+------------------+| group_concat(id) |+------------------+| 1 || 78,78 || 123 || 345 || 789 |+------------------+5 rows in set (0.00 sec)
三.参数设置与限制说明 1.查看服务器中设置 mysql> show variables like '%group_concat%';+----------------------+-------+| Variable_name | Value |+----------------------+-------+| group_concat_max_len | 1024 |+----------------------+-------+1 row in set (0.00 sec)以上设置的值说明当前是默认长度1KB 2.改变参数值 方法一：修改配置文件中参数，新增 group_concat_max_len = 10240 方法二：在会话中实现，全局或当前session中 SET GLOBAL group_concat_max_len=10240; SET SESSION group_concat_max_len=10240; 作者 kenyon bitsCN.com
