Sum custom field values of particular taxonomy

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I need to sum custom field values of a custom post type with a particular taxonomy ONLY.

For example…

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  • Custom Post Type: Computers
  • Taxonomy: Laptops
  • Custom Field: Quantity

How can I get the quantity value of “laptop” “computers” only?
I have been using the following to sum custom fields of ALL taxonomies… can it be modified to restrict to certain taxonomies? 

$total_quantity = array();
$meta_key = 'inventory-quantity'; //custom field meta key
$total_quantity = $wpdb->get_col($wpdb->prepare("SELECT meta_value FROM $wpdb->postmeta WHERE meta_key = %s", $meta_key));
echo 'QTY '.array_sum( $total_quantity );

Also just tried this as suggested and get a value of 0 returned.. 

$total_puppies = array();
$meta_key = 'wpcf-litter-puppies';//set this to your custom field meta key
$total_puppies = $wpdb->get_col($wpdb->prepare
("SELECT meta_value FROM wp_postmeta as pm
INNER JOIN wp_term_relationships as tr ON (pm.post_id = tr.object_id) 
INNER JOIN wp_term_taxonomy as tt ON (tr.term_taxonomy_id = tt.term_taxonomy_id) 
WHERE 1
AND tt.taxonomy = 'litter-type'
AND pm.meta_key = %s", 
$meta_key));
echo 'Total Puppies '.array_sum( $total_puppies );
Post Views: 2

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2 comments

  1. You would have to JOIN a couple of tables.

    SELECT meta_value FROM wp_postmeta as pm
INNER JOIN wp_term_relationships as tr ON (pm.post_id = tr.object_id) 
INNER JOIN wp_term_taxonomy as tt ON (tr.term_taxonomy_id = tt.term_taxonomy_id) 
WHERE 1
AND tt.taxonomy = 'laptop'
AND pm.meta_key = 'quantity'

    I am fairly sure that is right. These things are complicated.

    If your meta_value is a number– that is, no punctuation or other spaces– you should be able to use SUM(meta_value) and avoid the array_sum after the fact.

  2. I couldn’t get the SQL statements to work so I came up with another approach (not the best way to do this, but it works)…

    <?php 
$args = array(
    'post_type' => 'puppies',
    'taxonomy' => 'litter-type',
    'term' => 'previous-litters',
    'posts_per_page' =>-1
);
$loop = new WP_Query($args);
if ( $loop->have_posts() ) : ?> 
<?php    
while ( $loop->have_posts() ) : $loop->the_post(); ?>
    <?php $amt = get_post_meta($post->ID, 'wpcf-litter-puppies', true); ?> 
    <?php if ($amt) {$previous_puppies_total += $amt;}; ?>
    echo $total; ?>
<?php endwhile; ?>
<?php echo 'Puppies from previous litters: '.$previous_puppies_total; ?>
<?php endif; ?>
<?php wp_reset_postdata(); ?>

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