无法添加外键约束

Question

当我尝试创建一个名为Sales的表时,MySQL会出现以下错误.我不知道问题是什么,我瞥了一眼http://dev.mysql.com/doc/refman/4.1/en/innodb-foreign-key-constraints.html,看看我犯了什么错,但是我说不出来.我在MySQL 5.6.11中遇到此错误,但在5.1.67中没有

Error
SQL query:

CREATE TABLE IF NOT EXISTS Sales(

name VARCHAR( 30 ) NOT NULL ,
address VARCHAR( 70 ) NOT NULL ,
serialsold VARCHAR( 20 ) UNIQUE NOT NULL ,
background_check VARCHAR( 9 ) NOT NULL ,
soldfor FLOAT NOT NULL ,
datesold TIMESTAMP DEFAULTNOW( ) ,
FOREIGN KEY ( serialsold ) REFERENCES Guns( serialnumber ) ON DELETE SET NULL ON UPDATE CASCADE ,
PRIMARY KEY ( background_check )
);

MySQL said: Documentation

#1215 - Cannot add foreign key constraint 

我的枪支和购买表:

CREATE TABLE IF NOT EXISTS Purchases
(
    name          VARCHAR(30) NOT NULL,
    address       VARCHAR(70) NOT NULL,
    serialbought  VARCHAR(20) UNIQUE NOT NULL,
    boughtfor     FLOAT,
    datebought    TIMESTAMP DEFAULT NOW(),
    PRIMARY KEY (serialbought)
);

CREATE TABLE IF NOT EXISTS Guns
( 
  sequence      INTEGER(4)  NOT NULL AUTO_INCREMENT,
  manufacturer  VARCHAR(30) NOT NULL,
  model         VARCHAR(20) NOT NULL,
  caliber       VARCHAR(10) NOT NULL,
  serialnumber  VARCHAR(20) UNIQUE NOT NULL,
  type          VARCHAR(10) NOT NULl,
  sellsfor      FLOAT DEFAULT NULL,
  FOREIGN KEY (serialnumber) REFERENCES Purchases(serialbought)
    ON DELETE RESTRICT ON UPDATE RESTRICT,
  PRIMARY KEY (sequence)
);

Answer 1

您将字段定义serialsold为不可为空 -

serialsold VARCHAR( 20 ) UNIQUE NOT NULL

但是你试图用SET NULL子句添加动作 -

ON DELETE SET NULL

更改其中一个选项并尝试创建表.