从一个表中选择多个列并作为行插入另一个表

Question

我有两个表用户和电子邮件：

USER
+--------+-------+--------+--------+
| id (PK)| email | email2 | email3 |
+--------+-------+--------+--------+

EMAIL
+---------+--------------+---------------+
| id (PK) | user_id (FK) | email_address | 
+---------+--------------+---------------+

我需要从users表中选择电子邮件，然后将它们作为行插入到电子邮件表中。

Answer 1

如果您的电子邮件表ID具有身份，我会像这样做

INSERT INTO email (userid,email_address)
SELECT id, email  FROM user
UNION SELECT id, email2  FROM user
UNION SELECT id, email3 FROM user

Answer 2

使用union来做到这一点。

insert into email values(
select user_id, email from user
union
select user_id, email1 from user
union
select user_id, email2 from user
union
select user_id, email2 from user
)