最好的方法可能是：

global $wpdb;
$count = $wpdb->get_row("SELECT COUNT(*) AS THE_COUNT FROM $wpdb->postmeta WHERE (meta_key = \'color\' AND meta_value = \'blue\')");

return $count->THE_COUNT;

    /**
     * Returns the number of posts a particular metakey is used for.
     * Optionally qualified by a specific value or values in an array of the meta key.
     *
     * @param string            $key
     * @param null|string|array $value
     *
     * @return mixed
     */
    function get_meta_count( $key, $value = null) {
        global $wpdb;

        $where = get_meta_where($key, $value);
        $count = $wpdb->get_row("SELECT COUNT(*) AS THE_COUNT FROM $wpdb->postmeta WHERE $where");
        return $count->THE_COUNT;
    }

    /**
     * Returns the postmeta records for a particular metakey.
     * Optionally qualified by a specific value or values in an array of the meta key.
     *
     * @param string            $key
     * @param null|string|array $value
     *
     * @return mixed
     */
    function get_meta ( $key, $value = null) {
        global $wpdb;
        $where = get_meta_where($key, $value);
        return $wpdb->get_results("SELECT * FROM $wpdb->postmeta WHERE $where");
    }

    /**
     * Returns the where string for a metakey query
     *
     * @param string            $key
     * @param null|string|array $value
     *
     * @return string
     */
    function get_meta_where( $key, $value) {
        $where = "meta_key = \'$key\'";

        if (null !== $value) {
            if (\\is_array($value)) {
                \\array_walk($value,\'add_quote\');
                $in = \\implode(\',\', $value);  // Seperate values with a comma
                $where .= " AND meta_value IN ($in)";
            } else {
                $where .= " AND meta_value = \'$value\'";
            }
        }

        return $where;
    }

    /**
     * Puts quotes around each value in an array when used as a callback function
     *
     * @param $value
     * @param $key
     */
    function add_quote( &$value, $key)
    {
        $value = "\'$value\'";
    }