因此，我作为项目需求试图将外键约束添加到数据库中，并且它第一次或在两个不同的表上运行，但是在尝试添加外键约束时，我在两个表上遇到错误。我收到的错误消息是：

错误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;