谜语？ MYSQL - 使用 JOIN 限制子查询。想要删除所有帖子，每个类别至少 100 个帖子，但多个类别中的一些帖子答案

【问题标题】：riddle? MYSQL - LIMIT in subquery using JOIN. Want to delete all posts except minimum 100 posts per category but some posts in several categories谜语？ MYSQL - 使用 JOIN 限制子查询。想要删除所有帖子，每个类别至少 100 个帖子，但多个类别中的一些帖子
【发布时间】：2021-10-05 06:19:38
【问题描述】：

你好，使用 mysql8 (8.0.23) 的 wordpress：

我想删除除每个类别至少 100 个帖子之外的所有帖子。所以在前端，我希望点击任何类别以显示至少 100 个帖子。

这似乎很容易，除非许多帖子存在于多个类别中。

所以对于 A 类，如果我删除所有 >100 的帖子，那么第 112 行的帖子可能也存在于 B 类中，但只是第 80 行，因此会被删除。

看到谜底了吗？

所以在测试中使用 4 个类别，我该怎么做

删除 A 类帖子 >100
但在 B 类中不
但在 C 类中不
但在 D 类中不

对于下面的示例，类别 A、B、C、D 的 ID (71,72,73,74) 在子查询中使用 LIMIT（必须使用 JOIN，因为子查询中不允许使用 LIMIT？）


SELECT * FROM wp_posts
 
    JOIN 
    (
        SELECT ID 
        FROM wp_posts 
        WHERE NOT 
        (wp_posts.ID IN ( SELECT object_id FROM wp_term_relationships WHERE term_taxonomy_id IN (72) ) ) 
        LIMIT 100
    ) d
    ON wp_posts.ID 
    IN (d.ID)
    
    JOIN 
       (
        SELECT ID 
        FROM wp_posts 
        WHERE NOT 
        (wp_posts.ID IN ( SELECT object_id FROM wp_term_relationships WHERE term_taxonomy_id IN (73) ) ) 
         LIMIT 100
         ) e
        ON wp_posts.ID 
        IN (e.ID)
   
    JOIN 
       (
        SELECT ID 
        FROM wp_posts 
        WHERE NOT 
        (wp_posts.ID IN ( SELECT object_id FROM wp_term_relationships WHERE term_taxonomy_id IN (74) ) ) 
         LIMIT 100
         ) f
        ON wp_posts.ID 
        IN (f.ID)

 
  WHERE 
        (wp_posts.ID IN ( SELECT object_id FROM wp_term_relationships WHERE term_taxonomy_id IN (71) ) ) 
        AND (wp_posts.post_type = 'post' ) 
GROUP BY wp_posts.ID 
ORDER BY wp_posts.post_date DESC
LIMIT 99999999
OFFSET 100

它有零行

感谢您的帮助！

【问题讨论】：

stackoverflow.com/help/minimal-reproducible-example
SELECT VERSION(); 报告什么？回答这个问题的人可能想知道您是否可以使用窗口函数。
@BillKarwin 哦，它的 MySQL 8.0.23
add a row_number window function and partion it b 100
请不要在不可读的评论中发布任何代码。此外，您的 Row_number 只有一个按日期排列的顺序，但它还需要一个 PaRTITION BY，这是您想要数百个的类别

标签： mysql wordpress join subquery limit

【解决方案1】：

解决了..但没有使用 LIMIT 和 JOIN。

感谢@nbk 的评论，我改用ROW_NUMBER() OVER。这在子查询中是允许的。我在这里将其作为“选择”语句而不是删除（用于测试）。

在此处使用四个类别，类别 ID 为 71、72、73 和 74。

SELECT wp_posts.*
FROM  wp_posts 
   
WHERE 

(wp_posts.post_type = 'post' AND wp_posts.post_status = 'publish')   
   
AND

-- posts discluded if under 100 most recent per category:
(

( wp_posts.ID NOT IN (SELECT ID FROM (SELECT ID, ROW_NUMBER() OVER (ORDER BY wp_posts.post_date DESC) AS rownumber
  FROM wp_posts
  WHERE (wp_posts.ID IN (SELECT object_id FROM wp_term_relationships WHERE term_taxonomy_id IN (71) ) ) 
AND (wp_posts.post_type = 'post' AND wp_posts.post_status = 'publish')  
) AS foo
WHERE rownumber <= 100
) 
)

AND

( wp_posts.ID NOT IN (SELECT ID FROM (SELECT ID, ROW_NUMBER() OVER (ORDER BY wp_posts.post_date DESC) AS rownumber
  FROM wp_posts
  WHERE (wp_posts.ID IN (SELECT object_id FROM wp_term_relationships WHERE term_taxonomy_id IN (72) ) ) 
AND (wp_posts.post_type = 'post' AND wp_posts.post_status = 'publish')  
) AS foo
WHERE rownumber <= 100
) 
)

AND

( wp_posts.ID NOT IN (SELECT ID FROM (SELECT ID, ROW_NUMBER() OVER (ORDER BY wp_posts.post_date DESC) AS rownumber
  FROM wp_posts
  WHERE (wp_posts.ID IN (SELECT object_id FROM wp_term_relationships WHERE term_taxonomy_id IN (73) ) ) 
AND (wp_posts.post_type = 'post' AND wp_posts.post_status = 'publish')  
) AS foo
WHERE rownumber <= 100
) 
)

AND

( wp_posts.ID NOT IN (SELECT ID FROM (SELECT ID, ROW_NUMBER() OVER (ORDER BY wp_posts.post_date DESC) AS rownumber
  FROM wp_posts
  WHERE (wp_posts.ID IN (SELECT object_id FROM wp_term_relationships WHERE term_taxonomy_id IN (74) ) ) 
AND (wp_posts.post_type = 'post' AND wp_posts.post_status = 'publish')  
) AS foo
WHERE rownumber <= 100
) 
)

)

【讨论】：