mysql - 指向同一个表的多个外键 - 歧义问题

Question

我有一个 MySQL 数据库，其中包含两个外键的文章表：

• fk_id_user_created
• fk_id_user_edited

用户表如下所示

• pk_id_user
• 用户名

如何连接这些表，以便返回创建和编辑文章的用户的用户名？明显有歧义问题...

编辑：这显然不起作用：

SELECT
    articles.title,
    articles.article,
    users.username as created_by,
    users_username as edited_by
FROM
    articles
LEFT JOIN
    users
ON
    articles.fk_id_user_created = users.pk_id_username
LEFT JOIN
    users
ON
    articles.fk_id_user_edited = users.pk_id_username

Answer 1

加入users两次articles，提供一个别名来区分实例：

select  
  articles.whatever,
  created.username as created_username,
  edited.username as edited_username
from 
  articles
  inner join users as created on articles.fk_id_user_created = created.pk_id_user
  inner join users as edited  on articles.fk_id_user_edited  = edited.pk_id_user
;

Answer 2

你的意思是这样的，如果我理解正确的话？

CREATE TABLE USER (
user_id INTEGER PRIMARY KEY AUTO_INCREMENT,
username VARCHAR(255)
);

INSERT INTO USER (username) VALUES
('A'), ('B');

CREATE TABLE article (
id INTEGER PRIMARY KEY AUTO_INCREMENT,
user_id_created INTEGER,
user_id_edited INTEGER
);

INSERT INTO article (user_id_created, user_id_edited)
VALUES (1, 1), (2,1);

SELECT username 
FROM USER 
WHERE user_id IN (SELECT user_id_created FROM article WHERE user_id_created=user_id_edited);

DROP TABLE USER;
DROP TABLE article;

而且我没有使用连接，我只是假设 user_id_created 和 user_id_edited 是相同的。