Postgres查询以查找联结表中是否已存在组合

Question

我有一个简单的聊天模块，该模块允许帐户创建多用户房间。

• 给出以下架构-是否可以创建一个查询来检查给定用户的房间是否已存在？

• 如果此检查可能导致性能问题-您可以提出其他设计或方法吗？

示例数据：

- chat_id: 1, users: [1, 2, 3]
- chat_id: 2, users: [2, 3]
- chat_id: 3, users: [1]
- chat_id: 4, users: [5, 6]

所需查询：

Check if chat room for users [2, 3] exists => true, id: 2
Check if chat room for users [1, 2, 3] exists => true, id: 1
Check if chat room for users [2, 6] exists => false
Check if chat room for users [1, 2, 6] exists => false

我正在使用postgres 11.2

编辑： 如果给定的组合存在，我也应该能够获得聊天ID。

Answer 1

我认为这可以满足您的需求

select ca.chat_id
from chat_account ca
group by ca.chat_id
having count(*) filter (where account_id in (2, 3)) = 2 and
       count(*) = 2;

您还可以使用：

having array_agg(account_id order by account_id) = array[2, 3]

Answer 2

您需要这样的东西

with selected_users as (select * from accounts where id in (2,3)),
users_chat_rooms as (
select chat_id,
array_agg(account_id order by account_id asc) users_in_room
from chat_account
group by chat_id
)
select * from users_chat_rooms
where chat_id in (select chat_id from chat_account where account_id in (select id from selected_users))
and users_in_room = (select array_agg(id order by id asc) from selected_users)

请参见小提琴https://dbfiddle.uk/?rdbms=postgres_11&fiddle=f360a05c57a33f5c130fcfa0d55429ff

可能会将其显示给特定用户，因此您可以过滤“已登录”用户的聊天记录。

select * from users_chat_rooms
where chat_id in (select chat_id from chat_account where account_id = <logged_in_user>)
and users_in_room = (select array_agg(id order by id asc) from selected_users)

Answer 3

根据其他答案，我最终编写了自己的查询：

SELECT chat_id FROM chat_account
WHERE chat_id IN (
    SELECT c2.chat_id
    FROM chat_account c2
    WHERE c2.account_id IN (2, 3)
)
GROUP BY chat_account.chat_id
HAVING array_agg(chat_account.account_id) = ARRAY[2, 3]