查询以选择用户未注册的所有研讨会

Question

我想进行查询以选择用户未注册的所有研讨会信息。我希望拥有1个查询的所有数据。

这是：研讨会表 ：注册表 ：workshop_rounds表

希望你们中的一些人可以帮助我。 提前谢谢！

我已经尝试过这个查询，但这不是我想要的，它是接近但不完全。

SELECT * FROM `workshop_rounds` WHERE `id` != ALL (SELECT `workshop_round_id` FROM `registrations` WHERE `user_id` = 1) AND `workshop_id` != ALL (SELECT `workshop_id` FROM `workshop_rounds` WHERE `workshop_id`= ALL (SELECT `workshop_round_id` FROM `registrations` WHERE `user_id` = 1))

结果是：

但是现在我也希望不要使用与用户注册的轮次相同的workshop_id进行其他轮次。希望你能理解我。

Answer 1

对于单个用户，我会使用not exists：

来处理此问题

select w.*
from workshops w
where not exists (select 1
                  from registrations r
                  where r.workshop_id = w.id and
                        r.user_id = THE USER ID
                 );

Answer 2

使用NOT EXISTS

SELECT *
FROM workshops w
WHERE NOT EXISTS
(
    SELECT 1
    FROM registrations r
    JOIN "workshop_rounds" wr ON r."workshop_round_id" = wr.id
    WHERE wr.workshop_id = w.id
          AND r."user_id" = 1
);

也许更简洁NOT IN

SELECT *
FROM workshops w
WHERE w.id NOT IN
(
    SELECT wr.workshop_id
    FROM registrations r
    JOIN "workshop_rounds" wr ON r."workshop_round_id" = wr.id
    WHERE r."user_id" = 1
);

Answer 3

尝试使用此功能来获取用户未注册的所有研讨会

select ws.* from workshops ws 
       where ws.id not in (select w.id from workshops w, workshop_rounds wr, registrations r 
                where r.workshop_round_id = wr.id and wr.workshop_id=w.id and r.user_id = THE_USER_ID);