mysql - ALTER TABLE 问题

Question

我有一个问题，我想在表 bericht 中添加一个外键(电子邮件)。

电子邮件在 vrijwilliger 中引用电子邮件，电子邮件是 varchar(80)。

ALTER TABLE bericht
ADD(
FOREIGN KEY (email) REFERENCES vrijwilliger(email));

错误信息:

#1005 - Can't create table '.\c5g4westpopintranet#sql-1494_145.frm' (errno: 150)

我不明白，希望你能帮助我。

第一张 table

CREATE TABLE bericht(
berichtID int(8),
onderwerp varchar(255),
datum date,
tijd time,
inhoudbericht,
email varchar(80),
PRIMARY KEY(berichtID),
FOREIGN KEY(email) REFERENCES vrijwilliger(email));

第二张表

 CREATE TABLE vrijwilliger(
 vrijwilligerID int(8),
 email varchar(80),
 Primary key(vrijwilligerID));

Answer 1

尝试以下查询来更改表

ALTER TABLE bericht ADD CONSTRAINT email FOREIGN KEY(email) REFERENCES vrijwilliger(email) ON DELETE SET NULL ON UPDATE SET NULL;

修改表的语法

ALTER TABLE tbl_name
    ADD [CONSTRAINT [symbol]] FOREIGN KEY
    [index_name] (index_col_name, ...)
    REFERENCES tbl_name (index_col_name,...)
    [ON DELETE reference_option]
    [ON UPDATE reference_option]

引用

http://dev.mysql.com/doc/refman/5.5/en/innodb-foreign-key-constraints.html