mysql wpdb查询计数返回null

Question

我对mysql的wpdb查询返回null应该有一个匹配。

以下是我的代码

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

可能是您在查询中选择了多个值，而get_var只需要返回一个值。请尝试使用get_results。

Answer 2

您可以使用此处加入

$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);