public function _myplugin_user_edit_user_page()
{
    global $wpdb;
    $table_name = 'myplugin_users';
    if(isset($_GET['operation'])){
        if($_GET['operation'] == 'delete'){
            $wpdb->delete( $table_name, array( 'myplugin_user_id' => $_GET['id']) );
        }
    }
}

public function _myplugin_user_registration()
{
    global $wpdb;
    $table_name = 'myplugin_users';

    if( get_option('myplugin_user_option_name') != null){
        $myplugin_user_name = get_option('myplugin_user_option_name')['myplugin_user_first_name'];
        $myplugin_user_first_name = get_option('myplugin_user_option_name')['myplugin_user_first_name'];
        $myplugin_user_last_name = get_option('myplugin_user_option_name')['myplugin_user_last_name'];
        $myplugin_user_email = get_option('myplugin_user_option_name')['myplugin_user_email'];
        $random_password = wp_hash_password( wp_generate_password( $length=12, $include_standard_special_chars=false ) );

        $get_user = $wpdb->get_results('SELECT myplugin_user_login FROM myplugin_users WHERE myplugin_user_email="' . $myplugin_user_email . '" LIMIT 1', ARRAY_A);
        $user_exist = array_column($get_user, 'myplugin_user_login');
        if( !in_array($myplugin_user_name, $user_exist) ){
            $wpdb->insert(
                $table_name,
                array(
                    'myplugin_user_login' => $myplugin_user_name,
                    'myplugin_user_first_name' => $myplugin_user_first_name,
                    'myplugin_user_last_name' => $myplugin_user_last_name,
                    'myplugin_user_pass' => $random_password,
                    'myplugin_user_nice_name' => $myplugin_user_name,
                    'myplugin_user_email' => $myplugin_user_email,
                    'myplugin_user_url' => null,
                    'myplugin_user_registrated' => current_time( 'mysql' ),
                    'myplugin_user_activation_key' => null,
                    'myplugin_user_status' => 0,
                    'myplugin_display_name' => $myplugin_user_name
                )
            );
        }
    } else {
        $user_error_msg['_myplugin_existing_user_email'] = 'The user is already registered!';
    }
}