查找在 X 范围日期内发表第一条评论的帖子数

Question

我在尝试进行此查询时遇到问题，

我有 2 个表，我们称它们为帖子和评论：

帖子：

id	title	is_public
1	post 1	true
2	post 2	true
3	post 3	false

评论：

id	post_id	text	created_at
1	1	comment 1	2021-01-01
2	1	comment 2	2021-01-02
3	2	comment 3	2021-01-03
4	2	comment 4	2021-01-04
5	3	comment 5	2021-01-04

我要计算的是在 2 个日期之间创建第一条评论且帖子的变量 'is_public' 为真时的帖子数。

我已经查询了按日期排序评论并按 post_id 分组，但我不确定它是否正确：

SELECT COUNT(*) 
FROM (SELECT distinct on (c.post_id) c.post_id, c.created_at
FROM comments c
INNER JOIN posts p
ON p.id = c.post_id
WHERE c.created_at >= '2021-01-01' AND c.created_at <= '2021-01-04' AND p.is_public = true
ORDER BY c.post_id, c.created_at ASC) as q1;

日期为“2021-01-01”和“2021-01-04”的预期结果：

2

日期为“2021-01-02”和“2021-01-04”的预期结果：

1

任何人都可以帮助我确认我的解决方案或提出另一个方案吗？

Answer 1

I want to calculate is the count of posts where its first comment was created between 2 dates and when the variable 'is_public' of the posts is true

这基本上是过滤：

select count(*)
from posts p
where p.is_public and
      (select min(c.created_at)
       from comments c
       where c.post_id = p.id
      ) between '2021-01-01' and '2021-01-04';

查找在 X 范围日期内发表第一条评论的帖子数

Find count of posts where the first comment were made at X range dates

sql

postgresql

activerecord