function collation()
{

    $sql = "show table status";
    $cms_arr = $this->db->fetch_all($sql);
    foreach ($cms_arr as $v){
        if($v['Collation'] != 'utf8mb4_general_ci'){
            echo $v['Name'].'<br/>';
            $sql = "ALTER TABLE {$v['Name']} CONVERT TO CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci;";
            $this->db->fetch_first($sql);
        }

    }
    exit('ok');
}