Question

鉴于以下架构，成员可以共享帖子的所有权：

member: id, name, ...
post_owner: member_id, post_id
post: id, created, ...

查找过去90天内没有发帖的用户，最有效的查询是什么。

我想到了这一点，但似乎效率低下：

select *
from member
where member_id not in (
    select member_id
    from post p
    join post_owner po on po.post_id = p.id
    where created > subdate(now(), 90))

假设post(created)和所有外键都有索引。

Answer 1

这是怎么回事？

SELECT m.id, m.name 
From post p
INNER JOIN post_owner po ON po.post_id = p.id AND
RIGHT JOIN member m ON m.id = po.member_id
where  DATE_SUB(CURRENT_DATE(), INTERVAL 90 DAY) <= created

Answer 2

SELECT m.id, m.name 
FROM member m 
LEFT JOIN post_owner po ON m.id = po.member_id 
LEFT JOIN post p ON po.post_id = p.id AND p.created >= DATE_SUB(CURRENT_DATE(), INTERVAL 90 DAY)
WHERE p.id IS NULL

提示：将p.created与常量进行比较，以便使用索引。

Answer 3

试试这个：

SELECT m.id, m.name 
FROM member m 
LEFT JOIN post_owner po ON m.id = po.member_id 
LEFT JOIN post p ON po.post_id = p.id AND DATEDIFF(CURRENT_DATE(), p.created) <= 90
WHERE p.id IS NULL

在多个联接中查找缺失行的有效方法

3 个答案: