一旦您无法知道get_the_category, 我建议遍历类别并填充两个数组，一个用于父级，一个用于子级。之后，如果父数组为空，则显示子数组，否则显示父数组：

$categories = get_the_category();
if ( ! empty($categories) ) {
  $parents = array();
  $children = array();
  foreach( get_the_category() as $cat ) {
    if ( $cat->parent == 0 ) {
      $parents[] = $cat;
    } else {
      $children[] = $cat;
    }
  }
  $toshow = ! empty($children) ? $children : $parents;
  $sep = \'\';
  if ( ! empty($toshow) ) { foreach( $toshow as $cat ) {
    echo $sep;
    echo \'<span class="\' . $cat->name .\'">\';
    echo \'<a href="\' . get_category_link($cat->term_id) . \'">\' . $cat->name . \'</a></span>\';
    $sep = \' / \';
  } }
}