List custom field values ​​in alphabetical order without repetition from the current category?

Question

I have this code:

global $wpdb;
$query = "SELECT DISTINCT meta_value 
                 FROM $wpdb->postmeta 
                 WHERE meta_key = 'product_brand' 
                 ORDER BY meta_value;";
$directors = $wpdb->get_results( $query );  
foreach( $directors as $director ) :
    echo $director->meta_value . ', ';
endforeach;

This code will show all meta values having the meta_key "product_brand". On category pages, what I want to do is list all unique meta values having the meta_key "product_brand" from the current category.

Answer 1

what you could do is: 1. get the list of all posts currently on the page 2. grab all the IDs of the posts 3. do the following query:

SELECT DISTINCT meta_value FROM $wpdb->postmeta WHERE meta_key = 'product_brand' AND post_id IN (3,9,10,15) ORDER BY meta_value;

where 3,9,10,15 are post ids that you've collected.