group_concat function not returning all values. one extra comma adding at the end of the data

solution is use the below code in your model

$this->db->simple_query(‘SET SESSION group_concat_max_len=1000000’);

refer the below link for more details
http://mydoubts.in/blog/group_concat-function-not-returing-all-values-in-mysql-it-returns-some-values-with-one-comma-at-the-end/