Question

我有2个表 User1 和 Relationship ，这是某种用户-朋友关系。我需要找到一个用户的所有朋友。

例如：我有一个ID=3用户，并且我需要查找与此用户拥有Relationship.STATUS = 1的所有用户。

仅供参考，我是SQL的初学者，所以我知道这是一个非常简单的任务，但我无法处理。

我尝试使用JOIN，但未成功。

SELECT *
FROM USER1
         RIGHT JOIN RELATIONSHIP R on USER1.USER1_ID = R.USER_ID_FROM OR USER1.USER1_ID = R.USER_ID_TO
WHERE R.USER_ID_FROM = :id
   OR R.USER_ID_TO = :id AND R.STATUS = :status AND USER1_ID != :id;

我的桌子：

TABLE USER1
(
    USER1_ID     NUMBER PRIMARY KEY,
    USER_NAME    NVARCHAR2(64),
    REAL_NAME    NVARCHAR2(64),
    EMAIL        NVARCHAR2(64),
    PHONE_NUMBER NVARCHAR2(64),
    BIRTH_DATE   TIMESTAMP,
    POST_ID      NUMBER,
    PASSWORD     NVARCHAR2(16)

);

TABLE RELATIONSHIP
(
    USER_ID_FROM NUMBER NOT NULL,
    USER_ID_TO   NUMBER NOT NULL,
    STATUS       SMALLINT DEFAULT 0,
    CONSTRAINT FK_USER_ONE FOREIGN KEY (USER_ID_FROM) REFERENCES USER1 (USER1_ID),
    CONSTRAINT FK_USER_TWO FOREIGN KEY (USER_ID_TO) REFERENCES USER1 (USER1_ID),
    CONSTRAINT PK_RELATIONSHIP PRIMARY KEY (USER_ID_FROM, USER_ID_TO)

);

Answer 1

哼哼不确定，但我会尝试这样的事情：

SELECT u.* FROM USER1 u LEFT JOIN RELATIONSHIP r ON r.USER_ID_FROM = :id AND r.STATUS = 1 AND u.USER1_ID = r.USER_ID_TO;

其中的id是您要查找朋友的用户的ID。

Answer 2

SELECT *
FROM USER1 U
LEFT JOIN RELATIONSHIP R ON R.USER_ID_FROM = U.ID AND R.[STATUS] = 1
LEFT JOIN USER1 F ON R.[USER_ID_TO] = F.[ID]
WHERE U.[Id] = your_id

然后仅过滤用户。使用左联接是因为用户可能没有任何朋友。而且我知道您想找到该用户以及该用户的任何朋友。

Answer 3

尝试一下：

(SELECT *
FROM USER1 u
LEFT JOIN RELATIONSHIP f ON u.USER1_ID = f.USER_ID_FROM
WHERE f.USER_ID_TO= 3 AND f.STATUS = 1)
union
(SELECT *
FROM USER1 o
LEFT JOIN RELATIONSHIP t ON o.USER1_ID = t.USER_ID_TO
WHERE t.USER_ID_FROM= 3 AND t.STATUS = 1)

Answer 4

如果您只想要ID，则可以使用条件逻辑来选择哪个用户ID：

select (case when user_id_from = 1 then user_id_to else user_id_from
        end) as other_user_id
from relationship r
where 1 in (user_id_from, user_id_to) and
      status = 3;

如果您实际上需要所有用户信息，我建议您使用exists：

select u.*
from user1 u
where exists (select 1
              from relationship r
              where r.status = 3 and
                    ( (r.user_id_from = 1 and r.user_id_to = u.id) or
                      (r.user_id_to = 1 and r.user_id_from = u.id)
                    )
             );

SQL SELECT复合主键

4 个答案: