Question

我很难从桌子上找到合适的排。我试图通过查找电子邮件来获取一些行，并且我希望将最后一封电子邮件发送给他们。我的疑问是：

select *
from persons p2, (
SELECT p.id,p.name,p.email
FROM persons p, emails e
WHERE p.id = e.person_id
) a
where a.email = p2.email

此查询返回发送给个人的所有电子邮件的列表。

有人可以帮我查询此查询，查询需要返回带有电子邮件的人员列表，但每封电子邮件需要出现一次。

谢谢

Answer 1

尝试此变体：

select p.*, tmp.email
  from persons p, (select person_id, email
                     from emails e1
                    where not exists (
                          select 1
                            from emails e2
                           where e1.person_id = e2.person_id
                             and e1.time_sent < e2.time_sent)) tmp
 where p.id = tmp.person_id;

Answer 2

如果您的DBMS支持ctes，您可以执行以下操作：

;WITH CTE
AS
(
SELECT
    RANK() OVER(PARTITION BY person_id ORDER BY time_sent DESC) AS iRank,
    e.email,
    e.person_id
FROM
    email AS e
)
SELECT
    *
FROM
    persons AS p
    LEFT JOIN CTE
        ON p.id=CTE.person_id
        AND CTE.iRank=1

Answer 3

这个怎么样？

select *
from persons, (SELECT p.id, m.mail, max(m.time_sent) 
               from persons as p, emails as m 
               where m.mail = p.mail
               GROUP BY p.id, m.mail) as a
where persons.id = a.id

如何从表中获取每个电子邮件出现一次的行

3 个答案: