mysql - 如何比较父表和子表

Question

我有三个表:crawl_post、crawl_image 和crawl_video。

创建表crawl_post ( Id int NOT NULL AUTO_INCRMENT, 图像计数 int, 视频计数 int 主键(ID) );

创建表crawl_image ( Id int NOT NULL AUTO_INCRMENT, 状态 bool 值 帖子 ID 整数 主键(ID) );

创建表crawl_video ( Id int NOT NULL AUTO_INCRMENT, 状态 bool 值 帖子 ID 整数 主键(ID) );

状态 = true - 已下载，false - 未下载

通过查询，我想选择所有下载了图像和视频的帖子？这意味着，count(下载的图像) = post.Imagecount 和 count(下载的视频) = post.VideoCount。

感谢您的帮助。

Answer 1

使用join子句很容易实现这一点，如下所示:

select
    c1.*
from
    crawl_post c1
join
    crawl_image c2 on c1.id = c2.postid and c2.status = 1
join
    crawl_video c3 on c1.id = c3.postid and c3.status = 1

上面的 SQL 将返回所有下载了图像和视频的帖子的结果。

好吧，我试图理解你想要什么，你只是想获得完成所有图像和视频下载操作的帖子，对吗？我重新编辑如下:

select cp.* from (
select
    c1.id,
    count(c2.postid) as imageFinishedCount
    count(c3.postid) as videoFinishedCount
from
    crawl_post c1
left join
    crawl_image c2 on c1.id = c2.postid and c2.status = 1
left join
    crawl_video c3 on c1.id = c3.postid and c3.status = 1
group by
    c1.id
) tmp 
join 
    crawl_post cp on tmp.id = cp.id 
where 
    tmp.imageFinishedCount = cp.imageCount and tmp.videoFinishedCount = cp.videoCount