相关疑难解决方法(0)

CREATE DATABASE my_db;

CREATE TABLE class (
  classID int NOT NULL AUTO_INCREMENT,
  nameClass varchar(255),
  classLeader varchar(255),
  FOREIGN KEY (classLeader) REFERENCES student(studentID),
  PRIMARY KEY (classID));

CREATE TABLE student (
  studentID int NOT NULL AUTO_INCREMENT,
  lastName varchar(255),
  firstName varchar(255),
  classID int,
  FOREIGN KEY (classID) REFERENCES class(classID),
  PRIMARY KEY (studentID));

我试图通过使用外键确保表之间的数据一致性,以便DBMS可以检查错误; 然而,似乎我们不能出于某种原因这样做.什么是错误,有替代方案吗？另外,当我填写一个有外键的表时,我无法填写为外键保留的字段,对吗？是否外键被认为是关键？

我正在尝试为健身房管理系统创建数据库,但我无法弄清楚为什么我会收到此错误.我试图在这里寻找答案,但我找不到它.

ERROR 1215 (HY000): Cannot add foreign key constraint

CREATE TABLE sales(
    saleId int(100) NOT NULL AUTO_INCREMENT,
    accountNo int(100) NOT NULL,
    payName VARCHAR(100) NOT NULL,
    nextPayment DATE,
    supplementName VARCHAR(250),
    qty int(11),
    workoutName VARCHAR(100),
    sDate datetime NOT NULL DEFAULT NOW(),
    totalAmount DECIMAL(11,2) NOT NULL,
    CONSTRAINT PRIMARY KEY(saleId, accountNo, payName),
    CONSTRAINT FOREIGN KEY(accountNo) REFERENCES accounts(accountNo) ON DELETE CASCADE ON UPDATE CASCADE,
    CONSTRAINT FOREIGN KEY(payName) REFERENCES paymentFor(payName) ON DELETE CASCADE ON UPDATE CASCADE,
    CONSTRAINT FOREIGN KEY(supplementName) REFERENCES supplements(supplementName) ON DELETE CASCADE ON UPDATE …