使用posts_groupby的WordPress wp_query过滤器-如何计算联接表中的值？

Question

try to join my custom table to WP_Query, here is my wp_query code

     $the_query = new WP_Query( array('post_type'=> $post_type, 'paged' => $paged ,'posts_per_page' => 1, 'meta_query' => $meta_query, 'tax_query' => $tax_query, 'post_status' => 'publish', 'follower_id' => '') );

if ( $the_query->have_posts() ) : while ( $the_query->have_posts() ) : $the_query->the_post(); 

I saw the online tutorial said there I can join my custom table to the wp_query, using posts_join, posts_group, posts_where WordPress filter.

my problem is having a custom table, which calls wp_order_history

ID      post_id      order_number
1       211          AFD123D342234
2       211          dsafa23411414
3       110          sdafsaf234234
4       211          sdafasdfadsfs

there is the SQL code I want to merge to wp_query

LEFT JOIN(Select count(post_id), post_id as total_order From wp_order_history as oh WHERE oh.post_id = $wpdb->post_id group by post_id)

here I try to usings posts_where filter but not working :(

function custom_posts_where($where) {
            global $wpdb;
            $table_name = $wpdb->prefix . 'order_history';
            $where .= $wpdb->prepare("LEFT JOIN(Select count(post_id), post_id as total_order From wp_order_history as oh WHERE oh.post_id = $wpdb->post_id group by post_id)");
            return $where;
        }
add_filter('posts_where', 'custom_posts_where');

The result I want to get in the wp_query loop, count the total of orders each business have.

UPDATE, seem like code running through, but how can i output this? inside the wp_query loop? $the_query->total?

add_filter( 'posts_join', 'custom_posts_join', 10, 2 );
    function custom_posts_join( $join, $query ) {

        global $wpdb;
        //* if main query and search...
        // if ( is_main_query() && is_search() ) {

            //* join term_relationships, term_taxonomy, and terms into the current SQL where clause
            $join .= "
                LEFT JOIN 
                    (SELECT count(b.post_id) as total, b.post_id FROM wp_order_history as b group by b.business_id) as c
                ON c.post_id = $wpdb->posts.ID ";

        // }
        return $join;

    }

problem solve, thanks Hobo

Answer 1

Combining your code with my comments (NB: the inner query in the join function is different to yours - the example table you posted doesn't have a business_id column):

add_filter( 'posts_join', 'custom_posts_join', 10, 2 );
function custom_posts_join( $join, $query ) {

    global $wpdb;
    //* if main query and search...
    // if ( is_main_query() && is_search() ) {

        //* join term_relationships, term_taxonomy, and terms into the current SQL where clause

        $join .= "
            LEFT JOIN 
                (SELECT count(*) as total, b.post_id FROM {$wpdb->prefix}order_history as b group by b.post_id) as c
            ON c.post_id = $wpdb->posts.ID ";

    // }
    return $join;
}

add_filter( 'posts_fields', 'custom_posts_fields');
function custom_posts_fields( $sql ) {
    // c matches the table alias used in custom_posts_join().
    // The ifnull() function makes sure we have a value of 0 if the joined post is not in wp_order_history
    return $sql . ", ifnull(c.total,0) as total";
}

The value of the total column can then be accessed on the global $post variable. For example, in the loop:

<?php 
global $post;
if ( have_posts() ) :
    while ( have_posts() ) : the_post();
        print_r($post->total); // Field name should match the column name in the custom_posts_fields() function
    endwhile;
endif;
?>