尝试创建具有多个外键的表时收到外键约束错误

如何解决尝试创建具有多个外键的表时收到外键约束错误

CREATE TABLE IF NOT EXISTS 
Student_Clinic_STD_DB.Visit

 (
  `Room_id` INT NOT NULL,`P_ID` INT NOT NULL,`Dr_ID` INT(4) NOT NULL,`Time_Date` DATE NOT NULL,`N_ID` INT(6) NULL,PRIMARY KEY (`Time_Date`),INDEX `Room_Id` (`Room_id` ASC) VISIBLE,INDEX `Dr_id_idx` (`Dr_ID` ASC) VISIBLE,INDEX `N_Id_idx` (`N_ID` ASC) VISIBLE,FOREIGN KEY (`Dr_ID`)

    REFERENCES `Student_Clinic_STD_DB`.`Doctors` (`Dr_ID`));

    **FOREIGN KEY (`N_ID`)
    REFERENCES `Student_Clinic_STD_DB`.`Nurses` (`N_id`)**

ENGINE = InnoDB;

以粗体显示的行是引发错误的原因。该错误表明外来人在此职位无效，需要EOF，Alter等。