如何在wordpress查询中分解和组合值

I have a multiple pages in wordpress all with a single custom field called portfolio-section.

some examples of the data are

page 1 : portfolio-section = red
page 2 : portfolio-section = blue
page 3 : portfolio-section = red
page 4 : portfolio-section = red,blue

now im executing a wp query:

$querystr = "
    SELECT wposts.*
    FROM $wpdb->posts wposts, $wpdb->postmeta wpostmeta
    WHERE wposts.ID = wpostmeta.post_id
    AND wpostmeta.meta_key = 'portfolio-section'
    AND wposts.post_status = 'publish'
    ORDER BY wpostmeta.meta_value DESC
 ";
$pageposts = $wpdb->get_results($querystr, OBJECT);
 foreach ($pageposts as $post) {

 echo '<li><a rel="all '.get_post_meta($post->ID, 'portfolio-section', $single = true).'"><span>'.get_post_meta($post->ID, 'portfolio-section', $single = true).'</span></a></li>';

 }

which returns the values : "red", "blue", "red,blue"

however what i want to do is explode the "red,blue" and somehow combine it so the final list is

"red", "blue"

I'm not exactly sure what you're attempting to achieve but if you need to use explode to separate the "red,blue" it would be:

$colors = explode(',',$row);