这是返回自定义帖子类型列表的查询

$apartments = $wpdb->get_col( "
                SELECT DISTINCT( post_id ) 
                FROM $wpdb->postmeta 
                WHERE meta_key IN( $fields_string ) AND 
                      post_id IN ( SELECT ID FROM $wpdb->posts 
                      WHERE post_type = \'tvr_apartment\' AND 
                            post_status = \'publish\' ) 
                )" );

默认情况下，这首先返回最新的，我想随机排序；这就是我尝试的方式，但没有结果

$apartments = $wpdb->get_col( "
                SELECT DISTINCT( post_id ) 
                FROM $wpdb->postmeta 
                WHERE meta_key IN( $fields_string ) AND 
                      post_id IN ( SELECT ID FROM $wpdb->posts 
                      WHERE post_type = \'tvr_apartment\' AND 
                            post_status = \'publish\' ) 
                )
                ORDER BY $wpdb->postmeta.post_id rand()" );

我做错了什么？