汇总特定类别中所有帖子的元值

Question

I have a Nexus 4 category with a slug of: lg-nexus-4-e960

In this category, I have 100 posts. In the wp_postmeta table, each of these posts has a meta_field = sales_count, and a meta_value = 1, or more.

What I would like is to echo, outside the loop on a custom template, the total value of all the sales_count combined for that category. Essentially getting the amount of sales.

I have some idea of how it might work, but i do not have the knowledge to implement it. Query the wp_postmeta table, where the custom fields are being saved, and use the sum() sql function?

I tried this code, but it lacks a category specification:

<?php
$meta_key = 'sales_count';//set this to your custom field meta key
$allmiles=$wpdb->get_var($wpdb->prepare("SELECT sum(meta_value) FROM $wpdb->postmeta WHERE meta_key = %s", $meta_key));
echo '<p>Total miles is '.$allmiles . '</p>';
?>

Answer 1

Maybe not the most elegant solution

<?php

$catPost = get_posts(array('category' => get_cat_id("yourCategory"))); //change this
foreach ($catPost as $post) {
    setup_postdata($post);
    $ids[] = get_the_ID();
}

//we now have an array of ids from that category, so then
$idList = implode(",", $ids); //turn the array into a comma delimited list

$meta_key = 'sales_count';//set this to your custom field meta key
$allmiles = $wpdb->get_var($wpdb->prepare("
                                  SELECT sum(meta_value) 
                                  FROM $wpdb->postmeta 
                                  WHERE meta_key = %s 
                                  AND post_id in (" . $idList . ")", $meta_key));
echo '<p>Total miles is ' . $allmiles . '</p>';
?>

Answer 2

a faster way:

$allmiles = $wpdb->get_var($wpdb->prepare( 
            "SELECT sum( meta_value )
            FROM $wpdb->postmeta
            WHERE meta_key LIKE %s
            AND post_id
            IN ( 
            SELECT post_id
            FROM $wpdb->term_relationships
            WHERE term_taxonomy_id = %d
            )" , $meta_key , $cat_id ) );

Answer 3

For anyone still looking for more detailed solution, I have the following working based on the above answer by chiliNUT - Conditional based on page ID:

<?php if ( is_page( '123' ) ) { ?>/* change number */
<?php } elseif ( is_page( '321' ) ) { ?> /* change to different number */
<?php

$catPost = get_posts(array('post_type' => 'your_post_type', 'post_status' => array('publish', 'future'),'tax_query' => array(array('taxonomy' => 'your_cpt_categories', 'field' => 'slug', 'terms' => 'your-category-slug')))); //change these to suit your registered custom post type, taxonomies, post status, etc.
foreach ($catPost as $post) {
    setup_postdata($post);
    $ids[] = get_the_ID();
}

//we now have an array of ids from that category, so then
$idList = implode(",", $ids); //turn the array into a comma delimited list

$meta_key = 'your_meta_key';//set this to your custom field meta key
$allmiles = $wpdb->get_var($wpdb->prepare("
                                  SELECT sum(meta_value) 
                                  FROM $wpdb->postmeta 
                                  WHERE meta_key = %s 
                                  AND post_id in (" . $idList . ")", $meta_key));
echo '<p>Total miles is ' . $allmiles . '</p>';
?>

<?php } else { ?>

<?php the_content(); ?> /* or do other stuff */

<?php } ?>