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我有这个代码：

CREATE DATABASE IF NOT EXISTS courses;

USE 'courses'

CREATE TABLE IF NOT EXISTS teachers(
     id INT(10) UNSIGNED PRIMARY KEY NOT NULL AUTO_INCREMENT,
     name VARCHAR(50) NOT NULL,
     addr VARCHAR(255) NOT NULL,
     phone INT NOT NULL
)ENGINE=InnoDB DEFAULT CHARSET=utf8;

CREATE TABLE IF NOT EXISTS lessons(
     id INT PRIMARY KEY AUTO_INCREMENT NOT NULL,
     room TINYINT NOT NULL,
     length INT NOT NULL,
     lesson_date DATETIME NOT NULL,
     teacher INT NOT NULL,
     course INT NOT NULL,
     FOREIGN KEY(teacher) REFERENCES teachers(id),
     FOREIGN KEY(course) REFERENCES courses(id)
)ENGINE=InnoDB DEFAULT CHARSET=utf8;

CREATE TABLE IF NOT EXISTS courses(
      id INT PRIMARY KEY AUTO_INCREMENT NOT NULL,
      title VARCHAR(200) NOT NULL,
      length INT NOT NULL,
      description TEXT DEFAULT '',
      previous INT NOT NULL,
     FOREIGN KEY(previous) REFERENCES courses(id)
)ENGINE=InnoDB DEFAULT CHARSET=utf8;

执行此代码后，出现错误：Error 1005 (HY000) Can't create table 'courses.lessons' (errno: 150) 我做错了什么？

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1 回答 1

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你有两个问题。第一个是微不足道的：你不能在上面创建外键，lessons.course因为表还不存在，所以表创建失败。要解决此问题，请在create table课程后移动课程。

第二个问题是该列lessons.teacher与teacher.id. 外键只能在列具有相同类型时创建，并且您定义teacher.id为INT(10) UNSIGNEDwhile lessons.teacheris just INT（有符号，并且隐含长度 11）。将列的定义更改为lessons.teacher相同的类型：

teacher INT(10) UNSIGNED NOT NULL,
于 2013-09-11T17:19:09.670 回答