テーブルのカラムのコメント取得
/application/core/MY_Model.phpとかに実装
public function get_column_comments($table = '')
{
    if(empty($table)){
        $table = $this->name;
    }
    $query = "SELECT COLUMN_NAME,COLUMN_COMMENT FROM INFORMATION_SCHEMA.COLUMNS WHERE table_name = '$table' AND table_schema = '{$this->db->database}'";
    $result = $this->db->query($query);
    $result = $result->result('array');
    $tmp = array();
    foreach($result as $array){
        $tmp[$array['COLUMN_NAME']] = $array['COLUMN_COMMENT'];
    }
    return $tmp;
}