http://dev.mysql .com / doc / refman / 5.0 / en / group-by-functions.html#function_group-concat
SET [GLOBAL | SESSION] group_concat_max_len = val;
http://dev.mysql .com / doc / refman / 5.0 / en / group-by-functions.html#function_group-concat
SET [GLOBAL | SESSION] group_concat_max_len = val;