我试图将我的新模式转发到我的数据库服务器上,但我不知道为什么我会得到这个错误。

我试图在这里寻找答案,但我所找到的一切都表明,要么将数据库引擎设置为InnoDB,要么确保我试图用作外键的键是它们自己表中的主键。如果我没记错的话,这两件事我都做过。我还能做什么?

Executing SQL script in server

ERROR: Error 1215: Cannot add foreign key constraint

-- -----------------------------------------------------
-- Table `Alternative_Pathways`.`Clients_has_Staff`
-- -----------------------------------------------------
CREATE  TABLE IF NOT EXISTS `Alternative_Pathways`.`Clients_has_Staff` (
  `Clients_Case_Number` INT NOT NULL ,
  `Staff_Emp_ID` INT NOT NULL ,
  PRIMARY KEY (`Clients_Case_Number`, `Staff_Emp_ID`) ,
  INDEX `fk_Clients_has_Staff_Staff1_idx` (`Staff_Emp_ID` ASC) ,
  INDEX `fk_Clients_has_Staff_Clients_idx` (`Clients_Case_Number` ASC) ,
  CONSTRAINT `fk_Clients_has_Staff_Clients`
    FOREIGN KEY (`Clients_Case_Number` )
    REFERENCES `Alternative_Pathways`.`Clients` (`Case_Number` )
    ON DELETE NO ACTION
    ON UPDATE NO ACTION,
  CONSTRAINT `fk_Clients_has_Staff_Staff1`
    FOREIGN KEY (`Staff_Emp_ID` )
    REFERENCES `Alternative_Pathways`.`Staff` (`Emp_ID` )
    ON DELETE NO ACTION
    ON UPDATE NO ACTION)
ENGINE = InnoDB

SQL脚本执行完成:语句:7成功,1失败

下面是父表的SQL。

CREATE  TABLE IF NOT EXISTS `Alternative_Pathways`.`Clients` (
  `Case_Number` INT NOT NULL ,
  `First_Name` CHAR(10) NULL ,
  `Middle_Name` CHAR(10) NULL ,
  `Last_Name` CHAR(10) NULL ,
  `Address` CHAR(50) NULL ,
  `Phone_Number` INT(10) NULL ,
  PRIMARY KEY (`Case_Number`) )
ENGINE = InnoDB

CREATE  TABLE IF NOT EXISTS `Alternative_Pathways`.`Staff` (
  `Emp_ID` INT NOT NULL ,
  `First_Name` CHAR(10) NULL ,
  `Middle_Name` CHAR(10) NULL ,
  `Last_Name` CHAR(10) NULL ,
  PRIMARY KEY (`Emp_ID`) )
ENGINE = InnoDB

当前回答

In my case, I had deleted a table using SET FOREIGN_KEY_CHECKS=0, then SET FOREIGN_KEY_CHECKS=1 after. When I went to reload the table, I got error 1215. The problem was there was another table in the database that had a foreign key to the table I had deleted and was reloading. Part of the reloading process involved changing a data type for one of the fields, which made the foreign key from the other table invalid, thus triggering error 1215. I resolved the problem by dropping and then reloading the other table with the new data type for the involved field.

其他回答

你也可以检查两个表的Engine设置为InnoDB。

对我来说,1215错误发生在我导入mysqldump创建的dumpfile时,它按字母顺序创建了表,在我的例子中,这导致外键引用文件中稍后创建的表。(这篇博客文章指出:MySQL错误代码1215:“不能添加外键约束”)

由于mysqldump订单表字母顺序和我不想改变表的名字,我遵循的答案由JeremyWeir在本页上的说明,这说明要把设置FOREIGN_KEY_CHECKS = 0;把SET FOREIGN_KEY_CHECKS = 1;在转储文件的底部。

这个方法对我很有效。

你可能会得到外键约束错误的原因:

You are not using InnoDB as the engine on all tables. You are trying to reference a nonexistent key on the target table. Make sure it is a key on the other table (it can be a primary or unique key, or just a key) The types of the columns are not the same (an exception is the column on the referencing table can be nullable even if it is not nullable in the referenced table). If the primary key or foreign key is a varchar, make sure the collation is the same for both. One of the reasons may also be that the column you are using for ON DELETE SET NULL is not defined to be null. So make sure that the column is set default null.

检查这些。

另一个原因:如果你使用ON DELETE SET NULL,所有外键中的列都必须允许空值。有人在这个问题中发现了这一点。

从我的理解,这不会是一个关于数据完整性的问题,但似乎MySQL只是不支持这个功能(在5.7)。

此错误的另一个来源是当您有两个或多个具有相同外键名的相同表名时。

这种情况有时会发生在使用建模和设计软件(如MySQL Workbench),然后从设计中生成脚本的人身上。