如何加入（合并？）几个表？

Question

我有三张桌子

AUTHOR_TABLE
-------------
AUTHOR_ID (PK)   AUTHOR_NAME   
1                me
2                you 

ARTICLE_AUTHOR_TABLE
-------------
AUTHOR_ID  ARTICLE_ID  
1          100
2          101


EVENT_AUTHOR_TABLE
------------------------------------------
AUTHOR_ID   EVENT_ID  
1           200
1           201

我只想要一个

RESULTS
-----------------------------------------
AUTHOR_ID AUTHOR_NAME SOURCE_TABLE ID
1         me          article      100
2         you         article      101
1         me          event        200
1         me          event        201 

/* where SOURCE_TABLE would be either "EVENT" or "ARTICLE" */

编辑我真的不想要这个

RESULTS
-----------------------------------------
AUTHOR_ID AUTHOR_NAME EVENT_ID ARTICLE_ID
1         me          NULL         100
2         you         NULL         101
1         me          200         NULL
1         me          201         NULL

任何指针表示赞赏。

谢谢

Answer 1

SELECT A.AUTHOR_ID, A.AUTHOR_NAME, EA.EVENT_ID, AA.ARTICLE_ID
FROM AUTHOR_TABLE AS A
    LEFT JOIN ARTICLE_AUTHOR_TABLE AS AA ON AA.AUTHOR_ID = A.AUTHOR_ID
    LEFT JOIN EVENT_AUTHOR_TALBE AS EA ON EA.AUTHOR_ID = A.AUTHOR_ID

Answer 2

SELECT
  at.author_id,
  at.author_name,
  'article' AS source_table,
  aat.id
FROM
  author_table at
  JOIN article_author_table aat
    ON at.author_id = aat.author_id

UNION ALL

SELECT
  at.author_id,
  at.author_name,
  'event' AS source_table,
  eat.id
FROM
  author_table at
  JOIN event_author_table eat
    ON at.author_id = eat.author_id

Answer 3

因为这是家庭作业，我猜你正在使用 MySQL，read this documentation on the UNION syntax。您所做的基本上是从相似的数据库中执行两个（或更多）查询，并在一个查询中获取结果。

请注意，结果列必须相同。

您还可以创建变量来显示您从哪个表调用。

SELECT AUTHOR_ID, AUTHOR_NAME, `AUTHOR_TABLE` AS SOURCE_TABLE, ID FROM AUTHOR_TABLE

您这样做会影响所有联合，但会更改表名。