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.
artilla's personal blog. Sorry for broken English, just in practice