mysql wpdb查询计数返回空

Question

My wpdb query to mysql returning null where there should be one match.

Below is my code

global $wpdb;
$popular = $wpdb->get_var("
    SELECT COUNT(*)
    FROM $wpdb->postmeta AS pm, $wpdb->woocommerce_order_items AS woo
    WHERE (woo.order_id = pm.post_id AND pm.meta_value = 142)
");
var_dump($popular);

Answer 1

It may be that you're selecting multiple values in your query while get_var only expects a single value to be returned. Try using get_results instead.

Answer 2

You can use join here

$popular = $wpdb->get_var("SELECT COUNT(*) FROM $wpdb->postmeta AS pm left join $wpdb->woocommerce_order_items AS woo on(woo.order_id = pm.post_id)  WHERE pm.meta_value = 142");
var_dump($popular);