Make Display_name & Nickname Unique in WP

add_action('personal_options_update', 'check_display_name');
add_action('edit_user_profile_update', 'check_display_name');
function check_display_name($user_id) {
        global $wpdb;
        $unique = $wpdb->get_var($wpdb->prepare("SELECT COUNT(ID) FROM $wpdb->users WHERE display_name = %s AND ID <> %d", $_POST['display_name'], $_POST['user_id']));
        if($unique >=1) {
                $_POST['display_name'] = $_POST['username'];
                add_filter('user_profile_update_errors', 'check_dm_field', 10, 3);
        }
}

function check_dm_field($errors, $update, $user) {
        $errors->add('display_name_error',__('Sorry, Display Name is already in use. It needs to be unique.'));
        return false;
}
add_action('personal_options_update', 'check_nickname_name');
add_action('edit_user_profile_update', 'check_nickname_name');
function check_nickname_name($user_id) {
        global $wpdb;
        $unique = $wpdb->get_var($wpdb->prepare("SELECT COUNT(ID) FROM $wpdb->users as users, $wpdb->usermeta as meta
		 WHERE users.ID = meta.user_id
		 AND meta.meta_key = 'nickname'
		 AND meta.meta_value = %s
		 AND users.ID <> %d", $_POST['nickname'], $_POST['user_id']));
        if($unique >=1) {
                $_POST['nickname'] = $_POST['username'];
                add_filter('user_profile_update_errors', 'check_nick_field', 10, 3);
        }
}

function check_nick_field($errors, $update, $user) {
        $errors->add('nickname_error',__('Sorry, Nickname is already in use. It needs to be unique.'));
        return false;
}