change group_concat max len in mysql

When using group_concat in mysql, you may be embarrassed by truncated query results. Then, you should check the mysql variable, 'group_concat_max_len', it's default value is 1024.

   show variables like "group_concat_max_len";

The command, set group_concat_max_len = xxxx doesn't effect in my case. So I changed the config file in /etc/my.cnf,

 [mysqld]

 group_concat_max_len = xxxx

In addition, you should check 'max_allowed_packet' variable.