我对SQL查找没有任何附件的所有帖子的方式感到好奇。

方法#1-子查询NOT IN

这是我第一次尝试构造这样的查询：

global $wpdb;            
$sql = "
    SELECT  p1.ID, p1.post_title         
    FROM    {$wpdb->posts} p1
    WHERE   p1.post_type = \'post\'
        AND p1.post_status = \'publish\' 
        AND p1.ID NOT IN ( 
                SELECT DISTINCT p2.post_parent
                FROM {$wpdb->posts} p2
                WHERE p2.post_type = \'attachment\' AND p2.post_parent > 0  
        ) 
    ORDER BY p1.post_date DESC
";

// Fetch posts without attachments:
$posts_without_attachments = $wpdb->get_results( $sql );

// Display posts without attachments:
foreach( $posts_without_attachments as $post )
{
        echo $post->post_title . \'<br/>\';
}

这恰好与@toscho的查询非常相似，但在语法上没有那么精简；-）

方法#2-LEFT JOIN 具有IS NULL

此查询似乎也能正常工作：

global $wpdb;            
$sql = "
    SELECT  p1.ID, p1.post_title
    FROM {$wpdb->posts} p1 
    LEFT JOIN {$wpdb->posts} p2 
    ON ( p2.post_parent = p1.ID AND p2.post_type = \'attachment\' )
    WHERE p1.post_type =  \'post\' 
    AND p1.post_status =  \'publish\'
    AND p2.post_parent IS NULL 
    ORDER BY p1.post_date DESC
";

// Fetch posts without attachments:
$posts_without_attachments = $wpdb->get_results( $sql );

在这里，我们将posts表与其自身连接起来，然后选择NULL “附件”父列中的行。

方法#3-WP\\u查询posts\\u其中filter aka Method#1

我们还可以修改WP_Query() 使用posts_where 过滤器：

// Filter all posts without attachments:
add_filter( \'posts_where\', \'wpse_no_attachments\' );

// Query:
$q = new WP_Query( array( \'post_type\' => \'post\', \'posts_per_page\' => -1 ) );

// Remove the filter:
remove_filter( \'posts_where\', \'wpse_no_attachments\' );

其中：

function wpse_no_attachments( $where )
{
    global $wpdb;
    $where .= " AND {$wpdb->posts}.ID NOT IN (
                    SELECT DISTINCT wpse.post_parent
                    FROM {$wpdb->posts} wpse
                    WHERE wpse.post_type = \'attachment\' AND wpse.post_parent > 0  ) ";
    return $where;
}