Question

我有UPDATE次查询来更改videos表中所有id_video的记录状态（状态= 1），其中thumbnail的记录数为{{1} } {} thubmnails.status为1的表。

查询有效，但由于缩略图表的大小，它的速度非常慢。关于如何提高此查询速度的任何建议？

UPDATE videos 
SET    videos.status = 1 
WHERE  videos.id_video IN (SELECT thumbnails.id_video 
                           FROM   thumbnails 
                           WHERE  thumbnails.status = 1 
                           GROUP  BY thumbnails.id_video 
                           HAVING Count(thumbnails.id_thumbnail) = 10) 
       AND videos.status = 2;

在两个表格中都为id_video设置了索引。缩略图表的id_thumbnail。还有status列的索引。

Answer 1

我通过使您的查询更简单来删除IN子句

UPDATE videos v
SET v.status = 1
WHERE v.status = 2 AND (
    SELECT COUNT(t.id_thumbnail)
    FROM thumbnails t
    WHERE t.id_video = v.id_video AND t.status = 1
) = 10;

视频v记录只有在状态为2时才会更新，而且如果视频ID为v且状态为1，则会有10个缩略图t。

Answer 2

如果将IN子句转换为JOIN条件（如

），该怎么办？

UPDATE videos v
JOIN (SELECT thumbnails.id_video 
                           FROM   thumbnails 
                           WHERE  thumbnails.status = 1 
                           GROUP  BY thumbnails.id_video 
                           HAVING Count(thumbnails.id_thumbnail) = 10) xxx
ON v.id_video = xxx.id_video
SET v.status = 1 
WHERE v.status = 2;

Answer 3

您也可以尝试使用EXISTS代替IN：

UPDATE videos 
SET    videos.status = 1 
WHERE  videos.status = 2
AND EXISTS (SELECT thumbnails.id_video 
            FROM   thumbnails 
            WHERE  thumbnails.status = 1 
            GROUP  BY thumbnails.id_video 
            HAVING Count(thumbnails.id_thumbnail) = 10
            AND thumbnails.id_video = videos.id_video);

包含带子查询的IN的UPDATE查询非常慢

3 个答案: