Question

错误消息：＃1215 - 无法添加外键约束

你好我不能创建表外键...怎么做...我有两个表.. 第一个表有两个主键，第二个表是1个主键... 第一个表是 courseid varchar(5) 和courseyear int 第二个是subj_id varchar(5)

create table studentload(
student_id varchar(11) not null,
courseid varchar(5) not null,
courseyear int not null,
subj_id varchar(5) not null,
foreign key (courseid,courseyear) references course(courseid,courseyear),
foreign key (subj_id) references subject(subj_id)
)

修改

这是我已插入的所有表格

CREATE TABLE IF NOT EXISTS `course` (
  `courseid` varchar(5) NOT NULL,
  `courseyear` int(11) NOT NULL,
  `coursedesc` varchar(50),
  `subj_id` varchar(5) NOT NULL,
  PRIMARY KEY (`courseid`,`courseyear`)
) 


CREATE TABLE IF NOT EXISTS `subject` (
  `subj_id` varchar(5) NOT NULL,
  `subj_name` varchar(50) NOT NULL,
  `courseid` varchar(5),
  `courseyear` int(11),
  foreign key (`courseid`,`courseyear`) references `courseid` (`courseid`,`courseyear`)
)

Answer 1

这是样本SQLFiddle

您必须在primary key (subj_id)表

中添加studentload

在你的foriegn关系中，courseid不是tablename。它应该是

"references course(courseid,courseyear)"

像

CREATE TABLE IF NOT EXISTS `course` (
  `courseid` varchar(5) NOT NULL,
  `courseyear` int(11) NOT NULL,
  `coursedesc` varchar(50),
  `subj_id` varchar(5) NOT NULL,
  PRIMARY KEY (`courseid`,`courseyear`)
); 


CREATE TABLE IF NOT EXISTS `subject` (
  `subj_id` varchar(5) NOT NULL,
  `subj_name` varchar(50) NOT NULL,
  `courseid` varchar(5),
  `courseyear` int(11),
  foreign key (`courseid`,`courseyear`) references `course` (`courseid`,`courseyear`),
  primary key (`subj_id`)
);

create table studentload(
  student_id varchar(11) not null,
  courseid varchar(5) not null,
  courseyear int not null,
  subj_id varchar(5) not null,
  foreign key (courseid,courseyear) references course(courseid,courseyear),
  foreign key (subj_id) references subject(subj_id)
);

Answer 2

您使用过“引用courseid（courseid，courseyear）”。 courseid不是你的表名。它应该是“引用course（courseid，courseyear）”

Answer 3

有时是由于表创建的顺序。确保首先创建非外键表。

无法添加外键约束

3 个答案: