Question

我有以下表格结构，用于定义帖子及其类别之间的关系。

Post_id | Category_id
---------------------
1       | A
1       | B
1       | C
2       | A
2       | B
2       | C
2       | D

所以我想搜索有两个给定类别的帖子（例如A和B）然后删除A行。结果将是：

Post_id | Category_id
---------------------
1       | B
1       | C
2       | B
2       | C
2       | D

如何实现这一目标？

Answer 1

试试这个：

delete t1 
from yourtable t1
join (
    -- This sub query will retrieve records that have both A and B for each `Post_id`
    select Post_id
    from yourtable
    where Category_id in ('A', 'B')
    group by Post_id
    having count(distinct Category_id) = 2
) t2
-- Then join this sub query on your table.
on t1.Post_id = t2.Post_id
where t1.Category_id = 'A'

Demo Here

Answer 2

您可以通过以下方式找到帖子：

select post_id
from post_categories
where category_id in ('A', 'B')
group by post_id
having count(distinct category_id) = 2;

然后，您可以使用join

删除它们

delete pc
    from post_categories pc join
         (select post_id
          from post_categories
          where category_id in ('A', 'B')
          group by post_id
          having count(distinct category_id) = 2
         ) todelete
         on pc.post_id = todelete.post_id
    where pc.category_id = 'A';

删除多个位于同一个id的不同行的位置 - MySQL

2 个答案: