无法添加外键约束

Question

错误消息：#1215 - 无法添加外键约束

你好，我无法创建表外键......如何做到这一点......我有两个表......第一个表有两个主键然后第二个表是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)
)

编辑

这是我已经插入的所有表格

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

这是示例SQLFiddle

您必须在studentload表中添加primary key (subj_id)

在您的外国关系中，courseid 不是表名。 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

您已经使用了“参考courseid ( courseid , courseyear ) ”。 courseid 不是您的表名。 它应该是“参考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。