MySQL無法添加外鍵約束因此，我試圖將外鍵約束作為項(xiàng)目要求添加到我的數(shù)據(jù)庫中，并且它第一次或兩次在不同的表上工作，但是我有兩個(gè)表，當(dāng)我試圖添加外鍵約束時(shí)，會(huì)在兩個(gè)表上出錯(cuò)。我得到的錯(cuò)誤消息是：錯(cuò)誤1215(HY000)：無法添加外鍵約束這是我用來創(chuàng)建表的SQL，兩個(gè)違規(guī)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 = InnoDBDEFAULT 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 = InnoDBDEFAULT CHARACTER SET = utf8;