我启动了mysql并确认此查询返回一个结果：

mysql> SELECT * FROM wp_posts WHERE post_parent = 68 AND post_type = \'attachment\' AND post_name = \'side-logo-auto2\' LIMIT 1;
1 row in set (0.00 sec)

在我的模板中，我尝试了同样的事情：

<?php if ( have_posts() ) : while ( have_posts() ) : the_post();

    //$wpdb->posts is wp_posts table
    //$post->ID is current post of post_type page, 
    //that is associated with page of this template

    global $wpdb;
    $image = $wpdb->get_var(
        $wpdb->prepare(
            "SELECT * FROM $wpdb->posts
             WHERE post_parent = %d
             AND post_type = %s
             AND post_name = %s
             LIMIT 1
            ",
            $post->ID,
            \'attachment\',
            \'side-logo-auto2\'
        )
    );
    echo "The image id is {$image->ID}";
    echo wp_get_attachment_image($image->ID);

endwhile; endif; ?> 

$post->ID返回68。然而，分配给$image的值不是记录，而是空值。