Question

我有一个使用userid作为主键的成员资格表。

我有另一个表（表A），其中包含两个到membership（tableA.userid1和tableA.userid2）的外键。

现在我想使用userid1的电子邮件更新userid2的成员资格表中的电子邮件地址。

我该怎么做？有点像...

Update membership m2
set m2.email = m1.email
...???

Answer 1

UPDATE m2
SET email=m1.email
FROM TableA ta
INNER JOIN membership m1 ON ta.UserID1=m1.UserID
INNER JOIN membership m2 ON ta.UserID2=m2.UserID

Answer 2

 update A
     join membership as m1 on A.userid1 = m1.id
     join membership as m2 on A.userid2 = m2.id
 set m2.email = m1.email

，其中

create table membership (
  id int primary key auto_increment,
  email varchar(100)
);

create table A (
  userId1 int,
  userId2 int,
  constraint foreign key (userId1) references membership (id),
  constraint foreign key (userId2) references membership (id)
);

insert into membership (email) values
  ("user1@stackoverflow.com"),
  ("user2@stackoverflow.com");

insert into A values (1, 2);

update命令将用户2的电子邮件设置为用户1的电子邮件：

select * from membership;

id  email
1   user1@stackoverflow.com
2   user1@stackoverflow.com

以下是SQL Fiddle

的链接

使用（self？）连接更新

2 个答案: