因此，您不需要创建这些字段，这就是为什么它们被称为元字段，因为它们不需要任何设置。

我已经改进了代码并确保它正常工作，在这里和那里应用了一些好的实践，并添加了一些注释。

function custom_user_profile_fields( $user = null ) {
    global $wpdb;

    // This will check if we are dealing with the New User Page
    if ( $user instanceof WP_User ){
        // It\'s better to Just leave if the person doenst have permission
        if ( ! $user->exists() || ! current_user_can( \'edit_users\', $user->ID ) ) {
            return;
        }
    } elseif ( ! current_user_can( \'edit_users\' ) ) {
        return;
    }

    $meta = (object) array(
        \'client\' => \'\',
        \'group\' => \'\',
    );

    if ( $user instanceof WP_User ) {
        // Fetch the meta
        $meta->client = get_user_meta( $user->ID, \'client\', true );
        $meta->group = get_user_meta( $user->ID, \'user_groups\', true );
    }

    // Don\'t try to get info in the middle of the HTML (makes it harder to read the code later on)
    $usergroups = $wpdb->get_results( \'SELECT usergroup_name FROM wp_usergroup;\' );

    ?>
    <table class="form-table">
    <tr>
        <th><label for="company">Client Name</label></th>
        <td>
            <input type="text" class="regular-text" name="client" value="<?php echo esc_attr( $meta->client ); ?>" id="client" /><br />
        </td>
    </tr>
    <tr>
        <th><label for="company">User groups</label></th>
        <td>
        <select name="user_groups">
        <option>None</option>
            <?php foreach ( $usergroups as $group ) { ?>
                <option <?php selected( $meta->group, $group ); ?> value="<?php echo esc_attr( $group->usergroup_name );?>"><?php echo esc_html( ucfirst( $group->usergroup_name ) ); ?></option>
            <?php } ?>
        </select>
        </td>
    </tr>
    </table>
    <?php
}

add_action( \'show_user_profile\', \'custom_user_profile_fields\' );
add_action( \'edit_user_profile\', \'custom_user_profile_fields\' );
add_action( \'user_new_form\', \'custom_user_profile_fields\' );

function save_custom_user_profile_fields( $user_id ) {
    // again do this only if you can
    if ( ! current_user_can( \'edit_users\', $user_id ) ) {
        return;
    }

    if ( isset( $_POST[\'client\'] ) ) {
        update_user_meta( $user_id, \'client\', sanitize_text_field( $_POST[\'client\'] ) );
    } else {
        delete_user_meta( $user_id, \'client\' );
    }

    if ( isset( $_POST[\'user_groups\'] ) ) {
        update_user_meta( $user_id, \'user_groups\', sanitize_text_field( $_POST[\'user_groups\'] ) );
    } else {
        delete_user_meta( $user_id, \'user_groups\' );
    }
}
add_action( \'user_register\', \'save_custom_user_profile_fields\' );
add_action( \'personal_options_update\', \'save_custom_user_profile_fields\' );
add_action( \'edit_user_profile_update\', \'save_custom_user_profile_fields\' );