Sort column on meta key and meta value

Hello,

In the WordPress backend I’d like to sort a custom post type column on a meta key and meta value.

The meta key is called ‘status’. I’ve got three different meta value’s for the ‘status’ key. How can I sort them alphabetically?

This is my code:

// Register the column
function status_column_register( $columns ) {
    $columns['status'] = __( 'status', 'bf_rapportage' );

    return $columns;
}
add_filter( 'manage_edit-bf_rapportage_columns', 'status_column_register' );

// Display the column content
function status_column_display( $column_name, $post_id ) {
    if ( 'status' != $column_name )
        return;

    $status = get_post_meta($post_id, 'status', true);
    if ( !$status )
        $status = '<em>' . __( 'undefined', 'bf_rapportage' ) . '</em>';

    echo $status;
}
add_action( 'manage_posts_custom_column', 'status_column_display', 10, 2 );

// Register the column as sortable
function status_column_register_sortable( $columns ) {
    $columns['status'] = 'status';

    return $columns;
}
add_filter( 'manage_edit-bf_rapportage_sortable_columns', 'status_column_register_sortable' );

function status_column_orderby( $vars ) {
    if ( isset( $vars['orderby'] ) && 'status' == $vars['orderby'] ) {
        $vars = array_merge( $vars, array(
            'meta_key' => 'status',
            'orderby' => 'meta_value_num'
        ) );
    }

    return $vars;
}
add_filter( 'request', 'status_column_orderby' );