如何检索按日期SQL排序的分组消息

Question

让我假装我有以下“消息”表

ID (auto)   Sender     Receiver    Msg        Date (datetime)
1           Dave       John        Hi         01/01/2013
2           John       Dave        Hello      02/01/2013
3           James      Dave        U there?   02/02/2013
4           Dave       James       Yup        02/03/2013
5           Dave       Simon       Hey        02/03/2013

我想要Dave正在按照日期订购的人员名单。

Simon
James
John

我不知道如何在不查询“Dave”的情况下对它们进行分组。

非常感谢。

Answer 1

您似乎想要与Dave交谈的 distinct 人员列表：

select (case when receiver = 'Dave' then Sender else Receiver end)
from messages m
where 'Dave' in (Receiver, Sender)
group by (case when receiver = 'Dave' then Sender else Receiver end)
order max(date) desc;

Answer 2

这将给你每个人Dave已发送消息并收到按日期订购的消息。

SELECT DISTINCT(Receiver) FROM messages WHERE Sender = 'Dave' ORDER BY date DESC

Answer 3

SELECT Receiver FROM messages WHERE Sender = "Dave"
AND Receiver NOT IN (SELECT Sender FROM messages WHERE Receiver = "Dave")
UNION
SELECT Sender FROM messages WHERE Receiver = "Dave"