Question

我在表格中有一些数据：

用户

user_id  name
1        John
2        William
3        cindy
4        Julian
5        Monique

预订

user_id  book_id
1        1
2        3
3        5
5        10

黑胶唱片

user_id  vinyl_id
1        6
2        7
3        8
4        9

我想要一个能产生这个输出的SELECT语句：

user_id  item_out
1        1 
1        6
2        3
2        7
3        5     
3        8 
4        9
5        10

因此，按user_id和book_id / vinyl_id的顺序排列。这可能吗？

Answer 1

您必须从两个单独的查询中获得UNION ALL个结果：

SELECT u.user_id, book_id AS item_out
FROM user AS u
INNER JOIN books_out AS b ON u.user_id = b.user_id

UNION ALL

SELECT u.user_id, vinyl_id AS item_out
FROM user AS u
INNER JOIN vinyl_out AS v ON u.user_id = v.user_id
ORDER BY user_id, item_out

第一个查询返回books_out表的结果，而第二个查询返回vinyl_out表的结果。

注意： ORDER BY子句适用于UNION ALL操作生成的结果集。

Demo here

Answer 2

试试这个如果有任何错误请评论。

select u.user_id,b.book_id as item_out from user u left join 
 books_out b on u.user_id = b.user_id 
 UNION ALL
 select u.user_id,v.vinyl_id as item_out from user u left join 
 vinyl_out v on u.user_id = v.user_id 
 order by user_id;

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