[英]Checking the same values in two different columns of same table and then compare in sql
[英]How to get unique values to compare two columns of the same table?
目前,我正在使用 SQLite 處理 Django 項目,在該項目中我創建了一個消息聊天框,並且我想獲取登錄用戶的最新消息,無論它是發送還是接收。
id receiver_id sender_id message_content created_at
1 1 2 some text 2020-08-11 13:29:47.342944
3 3 2 some text 2020-08-11 13:44:55.499638
4 2 1 some text 2020-08-11 14:20:55.499638
5 1 2 some text 2020-08-12 05:06:05.497500
6 2 5 some text 2020-08-12 10:39:31.234082
7 4 1 some text 2020-08-14 13:25:19.357876
使用下面 SQL 查詢后。
SELECT max(created_at), *
FROM hireo_messages
WHERE receiver_id=2 or sender_id=2
GROUP BY receiver_id, sender_id
ORDER BY created_at DESC
我得到了以下結果。
id receiver_id sender_id message_content created_at
6 2 5 some text 2020-08-12 10:39:31.234082
5 1 2 some text 2020-08-12 05:06:05.497500
4 2 1 some text 2020-08-11 14:20:55.499638
3 3 2 some text 2020-08-11 13:44:55.499638
如您所見,id 5、4 都在互相聊天。 所以我想獲取除 id 4 之外的所有記錄,因為 2 個用戶之間的最新聊天在 id 5 中。它與 Facebook 信使儀表板中使用的概念相同。 請指導我是通過查詢解決還是使用任何其他方式。 在此先感謝您的幫助!
我想你想要:
SELECT LEAST(receiver_id, sender_id), GREATEST(receiver_id, sender_id), MAX(created_at)
FROM hireo_messages
WHERE 2 IN (receiver_id, sender_id)
GROUP BY LEAST(receiver_id, sender_id), GREATEST(receiver_id, sender_id)
ORDER BY MAX(created_at) DESC;
如果您想要完整的行,請使用 window 函數:
SELECT m.*
FROM (SELECT m.*,
ROW_NUMBER() OVER (PARTITION BY LEAST(receiver_id, sender_id), GREATEST(receiver_id, sender_id) ORDER BY created_at DESC) as seqnum
FROM hireo_messages m
WHERE 2 IN (receiver_id, sender_id)
) m
WHERE seqnum = 1
ORDER BY MAX(created_at) DESC;
您可以使用 window function MAX()
:
select id, receiver_id, sender_id, message_content, created_at
from (
select *,
max(created_at) over (partition by min(receiver_id, sender_id), max(receiver_id, sender_id)) last_date
from hireo_messages
where 2 in (receiver_id, sender_id)
)
where created_at = last_date
order by id desc
如果您的 SQLite 版本不支持 window 功能,您可以使用NOT EXISTS
:
select h.* from hireo_messages h
where 2 in (receiver_id, sender_id)
and not exists (
select 1 from hireo_messages
where min(receiver_id, sender_id) = min(h.receiver_id, h.sender_id)
and max(receiver_id, sender_id) = max(h.receiver_id, h.sender_id)
and created_at > h.created_at
)
order by h.id desc
請參閱演示。
結果:
| id | receiver_id | sender_id | message_content | created_at |
| --- | ----------- | --------- | --------------- | -------------------------- |
| 6 | 2 | 5 | some text | 2020-08-12 10:39:31.234082 |
| 5 | 1 | 2 | some text | 2020-08-12 05:06:05.497500 |
| 3 | 3 | 2 | some text | 2020-08-11 13:44:55.499638 |
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