ERROR 1822 (HY000): 添加外键约束失败。 SQL中的约束问题缺少索引[重复]

Question

我通过创建 3 个表 (classes, lectures, taking) 来创建数据库，然后更改表以添加 foreign key。

但是，我不断收到以下错误： ERROR 1822 (HY000): Failed to add the foreign key constraint. Missing index for constraint

我似乎没有发现代码有任何问题，那么可能是什么问题？ （我使用的是mySQL Workbench。我尝试复制粘贴为txt文件，因为我虽然可能是排序规则问题，但仍然会出现同样的问题）

代码如下：

CREATE TABLE classes (
    course_id VARCHAR(8),
    classes_id VARCHAR(10),
    semester VARCHAR(10),
    year VARCHAR(10),
    PRIMARY KEY (course_id, classes_id, semester, year)
);

CREATE TABLE taking (
    student_id VARCHAR(8),
    course_id VARCHAR(10),
    classes_id VARCHAR(10),
    semester VARCHAR(10),
    year VARCHAR(10),
    grade char(1),
    PRIMARY KEY (student_id, course_id, semester, year)
);

CREATE TABLE lectures (
    professor_id VARCHAR(8),
    course_id VARCHAR(10),
    classes_id VARCHAR(10),
    semester VARCHAR(10),
    year VARCHAR(10),
    PRIMARY KEY (professor_id, course_id, semester, year)
);

ALTER TABLE taking ADD CONSTRAINT consTAKE3 FOREIGN KEY(classes_id) REFERENCES classes(classes_id) ON DELETE CASCADE;
ALTER TABLE taking ADD CONSTRAINT consTAKE4 FOREIGN KEY(semester) REFERENCES classes(semester) ON DELETE CASCADE;
ALTER TABLE taking ADD CONSTRAINT consTAKE5 FOREIGN KEY(year) REFERENCES classes(year) ON DELETE CASCADE;

ALTER TABLE lectures ADD CONSTRAINT consLEC3 FOREIGN KEY(classes_id) REFERENCES classes(classes_id) ON DELETE CASCADE;
ALTER TABLE lectures ADD CONSTRAINT consLEC4 FOREIGN KEY(semester) REFERENCES classes(semester) ON DELETE CASCADE;
ALTER TABLE lectures ADD CONSTRAINT consLEC5 FOREIGN KEY(year) REFERENCES classes(year) ON DELETE CASCADE;

错误如下：

ERROR 1822 (HY000): Failed to add the foreign key constraint. Missing index for constraint 'consTAKE3' in the referenced table 'classes'
ERROR 1822 (HY000): Failed to add the foreign key constraint. Missing index for constraint 'consTAKE4' in the referenced table 'classes'
ERROR 1822 (HY000): Failed to add the foreign key constraint. Missing index for constraint 'consTAKE5' in the referenced table 'classes'
ERROR 1822 (HY000): Failed to add the foreign key constraint. Missing index for constraint 'consLEC3' in the referenced table 'classes'
ERROR 1822 (HY000): Failed to add the foreign key constraint. Missing index for constraint 'consLEC4' in the referenced table 'classes'
ERROR 1822 (HY000): Failed to add the foreign key constraint. Missing index for constraint 'consLEC5' in the referenced table 'classes'

现在，我正在尝试使用 ysql –u root –p 从 cmd 执行此操作。不过，同样的问题正在发生。

Answer 1

由于您在所有表中都有复合主键，因此所有引用还必须包含表中的所有复合键列才能正确映射。

除非您对每个表的复合主键列都有唯一约束/索引。

要在表中创建关系，请尝试对 dbo.taking 进行此操作，其他表也遵循类似的方法

ALTER TABLE dbo.taking 
  ADD CONSTRAINT FK_taking_classes
  FOREIGN KEY(course_id, classes_id, semester, year) REFERENCES classes(course_id, 
classes_id, semester, year)

Answer 2

两个表中course_id的字符长度不同，导致没有创建FK。请在与classes 相同的taking 表中将其设置为varchar(8)。它肯定会解决问题。我已经使用提供的查询创建了表并且还具有 FK。

然后按照上面提到的查询：

由于您在所有表中都有一个复合主键，所以所有 引用还必须包括所有复合键列 表来正确映射。

除非您在复合主键上有唯一的约束/索引 每个表上的列。

要在表格中创建关系，请尝试 dbo.taking，关注 其他表也采用类似方法

  ALTER TABLE dbo.taking 
  ADD CONSTRAINT FK_taking_classes
  FOREIGN KEY(course_id, classes_id, semester, year) REFERENCES classes(course_id, 
  classes_id, semester, year)