MySQL无法添加外键约束

Question

所以我试图将外键约束添加到我的数据库作为项目需求,它在不同的表上第一次或第二次工作,但我有两个表,在尝试添加外键约束时我得到一个错误.我得到的错误消息是:

ERROR 1215(HY000):无法添加外键约束

这是我用来创建表的SQL,两个有问题的表是Patient和Appointment.

SET @OLD_UNIQUE_CHECKS=@@UNIQUE_CHECKS, UNIQUE_CHECKS=0;
SET @OLD_FOREIGN_KEY_CHECKS=@@FOREIGN_KEY_CHECKS, FOREIGN_KEY_CHECKS=1;
SET @OLD_SQL_MODE=@@SQL_MODE, SQL_MODE='TRADITIONAL,ALLOW_INVALID_DATES';

CREATE SCHEMA IF NOT EXISTS `doctorsoffice` DEFAULT CHARACTER SET utf8 ;
USE `doctorsoffice` ;

-- -----------------------------------------------------
-- Table `doctorsoffice`.`doctor`
-- -----------------------------------------------------
DROP TABLE IF EXISTS `doctorsoffice`.`doctor` ;

CREATE  TABLE IF NOT EXISTS `doctorsoffice`.`doctor` (
  `DoctorID` INT(11) NOT NULL AUTO_INCREMENT ,
  `FName` VARCHAR(20) NULL DEFAULT NULL ,
  `LName` VARCHAR(20) NULL DEFAULT NULL ,
  `Gender` VARCHAR(1) NULL DEFAULT NULL ,
  `Specialty` VARCHAR(40) NOT NULL DEFAULT 'General Practitioner' ,
  UNIQUE INDEX `DoctorID` (`DoctorID` ASC) ,
  PRIMARY KEY (`DoctorID`) )
ENGINE = InnoDB
DEFAULT CHARACTER SET = utf8;


-- -----------------------------------------------------
-- Table `doctorsoffice`.`medicalhistory`
-- -----------------------------------------------------
DROP TABLE IF EXISTS `doctorsoffice`.`medicalhistory` ;

CREATE  TABLE IF NOT EXISTS `doctorsoffice`.`medicalhistory` (
  `MedicalHistoryID` INT(11) NOT NULL AUTO_INCREMENT ,
  `Allergies` TEXT NULL DEFAULT NULL ,
  `Medications` TEXT NULL DEFAULT NULL ,
  `ExistingConditions` TEXT NULL DEFAULT NULL ,
  `Misc` TEXT NULL DEFAULT NULL ,
  UNIQUE INDEX `MedicalHistoryID` (`MedicalHistoryID` ASC) ,
  PRIMARY KEY (`MedicalHistoryID`) )
ENGINE = InnoDB
DEFAULT CHARACTER SET = utf8;


-- -----------------------------------------------------
-- Table `doctorsoffice`.`Patient`
-- -----------------------------------------------------
DROP TABLE IF EXISTS `doctorsoffice`.`Patient` ;

CREATE  TABLE IF NOT EXISTS `doctorsoffice`.`Patient` (
  `PatientID` INT unsigned NOT NULL AUTO_INCREMENT ,
  `FName` VARCHAR(30) NULL ,
  `LName` VARCHAR(45) NULL ,
  `Gender` CHAR NULL ,
  `DOB` DATE NULL ,
  `SSN` DOUBLE NULL ,
  `MedicalHistory` smallint(5) unsigned NOT NULL,
  `PrimaryPhysician` smallint(5) unsigned NOT NULL,
  PRIMARY KEY (`PatientID`) ,
  UNIQUE INDEX `PatientID_UNIQUE` (`PatientID` ASC) ,
  CONSTRAINT `FK_MedicalHistory`
    FOREIGN KEY (`MEdicalHistory` )
    REFERENCES `doctorsoffice`.`medicalhistory` (`MedicalHistoryID` )
    ON DELETE CASCADE
    ON UPDATE CASCADE,
  CONSTRAINT `FK_PrimaryPhysician`
    FOREIGN KEY (`PrimaryPhysician` )
    REFERENCES `doctorsoffice`.`doctor` (`DoctorID` )
    ON DELETE CASCADE
    ON UPDATE CASCADE)
ENGINE = InnoDB;


-- -----------------------------------------------------
-- Table `doctorsoffice`.`Appointment`
-- -----------------------------------------------------
DROP TABLE IF EXISTS `doctorsoffice`.`Appointment` ;

CREATE  TABLE IF NOT EXISTS `doctorsoffice`.`Appointment` (
  `AppointmentID` smallint(5) unsigned NOT NULL AUTO_INCREMENT ,
  `Date` DATE NULL ,
  `Time` TIME NULL ,
  `Patient` smallint(5) unsigned NOT NULL,
  `Doctor` smallint(5) unsigned NOT NULL,
  PRIMARY KEY (`AppointmentID`) ,
  UNIQUE INDEX `AppointmentID_UNIQUE` (`AppointmentID` ASC) ,
  CONSTRAINT `FK_Patient`
    FOREIGN KEY (`Patient` )
    REFERENCES `doctorsoffice`.`Patient` (`PatientID` )
    ON DELETE CASCADE
    ON UPDATE CASCADE,
  CONSTRAINT `FK_Doctor`
    FOREIGN KEY (`Doctor` )
    REFERENCES `doctorsoffice`.`doctor` (`DoctorID` )
    ON DELETE CASCADE
    ON UPDATE CASCADE)
ENGINE = InnoDB;


-- -----------------------------------------------------
-- Table `doctorsoffice`.`InsuranceCompany`
-- -----------------------------------------------------
DROP TABLE IF EXISTS `doctorsoffice`.`InsuranceCompany` ;

CREATE  TABLE IF NOT EXISTS `doctorsoffice`.`InsuranceCompany` (
  `InsuranceID` smallint(5) NOT NULL AUTO_INCREMENT ,
  `Name` VARCHAR(50) NULL ,
  `Phone` DOUBLE NULL ,
  PRIMARY KEY (`InsuranceID`) ,
  UNIQUE INDEX `InsuranceID_UNIQUE` (`InsuranceID` ASC) )
ENGINE = InnoDB;


-- -----------------------------------------------------
-- Table `doctorsoffice`.`PatientInsurance`
-- -----------------------------------------------------
DROP TABLE IF EXISTS `doctorsoffice`.`PatientInsurance` ;

CREATE  TABLE IF NOT EXISTS `doctorsoffice`.`PatientInsurance` (
  `PolicyHolder` smallint(5) NOT NULL ,
  `InsuranceCompany` smallint(5) NOT NULL ,
  `CoPay` INT NOT NULL DEFAULT 5 ,
  `PolicyNumber` smallint(5) NOT NULL AUTO_INCREMENT ,
  PRIMARY KEY (`PolicyNumber`) ,
  UNIQUE INDEX `PolicyNumber_UNIQUE` (`PolicyNumber` ASC) ,
  CONSTRAINT `FK_PolicyHolder`
    FOREIGN KEY (`PolicyHolder` )
    REFERENCES `doctorsoffice`.`Patient` (`PatientID` )
    ON DELETE CASCADE
    ON UPDATE CASCADE,
  CONSTRAINT `FK_InsuranceCompany`
    FOREIGN KEY (`InsuranceCompany` )
    REFERENCES `doctorsoffice`.`InsuranceCompany` (`InsuranceID` )
    ON DELETE CASCADE
    ON UPDATE CASCADE)
ENGINE = InnoDB;

USE `doctorsoffice` ;


SET SQL_MODE=@OLD_SQL_MODE;
SET FOREIGN_KEY_CHECKS=@OLD_FOREIGN_KEY_CHECKS;
SET UNIQUE_CHECKS=@OLD_UNIQUE_CHECKS;

Answer 1

要查找特定错误,请执行以下操作:

SHOW ENGINE INNODB STATUS;

并查看该LATEST FOREIGN KEY ERROR部分.

子列的数据类型必须与父列完全匹配.例如,既然medicalhistory.MedicalHistoryID是INT,Patient.MedicalHistory也需要是INT,而不是SMALLINT.

此外,您应该set foreign_key_checks=0在运行DDL之前运行查询,以便您可以按任意顺序创建表,而不需要在相关子表之前创建所有父表.

Answer 2

我将一个字段设置为"未签名"而另一个字段不设置.一旦我将两列都设置为无符号就可以了.

Answer 3

• 引擎应该是相同的,例如InnoDB
• 数据类型应该相同,并且长度相同.例如VARCHAR(20)
• 整理列charset应该是相同的.例如utf8
  Watchout:即使你的表具有相同的Collat​​ion,列仍然可以有不同的列.
• 唯一 - 外键应引用参考表中唯一的字段(通常是主键).

Answer 4

尝试使用相同类型的主键 - int(11) - 在外键 - smallint(5) - 上.

希望能帮助到你!

Answer 5

确认两个表的字符编码和排序规则相同.

在我自己的情况下,其中一个表正在使用utf8,另一个表正在使用latin1.

我有另一种情况,编码是相同的但排序规则不同.一个utf8_general_ci其他utf8_unicode_ci

您可以运行此命令来设置表的编码和排序规则.

ALTER TABLE tablename CONVERT TO CHARACTER SET utf8 COLLATE utf8_unicode_ci;

我希望这可以帮助别人.

Answer 6

要在表B中设置FOREIGN KEY,必须在表A中设置KEY.

在表A中:INDEX id(id)

然后在表B中,

CONSTRAINT `FK_id` FOREIGN KEY (`id`) REFERENCES `table-A` (`id`)

Answer 7

我有同样的问题,解决方案很简单.解决方案:表中声明的外键不应设置为null.

reference:如果指定SET NULL操作,请确保未将子表中的列声明为NOT NULL.(参考 )