我的外键的PostgreSQL代码给出外键约束不存在[重复]

Question

我的代码：

create table courses(
id SERIAL PRIMARY KEY 
)
----------------------
create table teachers(
id SERIAL PRIMARY KEY 
)
----------------------

CREATE TABLE assignments(
    id SERIAL PRIMARY KEY ,
    given_date TIMESTAMP,
    deadline TIMESTAMP,
    FOREIGN KEY(course_id) REFERENCES courses(id),
    FOREIGN KEY(teacher_id) REFERENCES teachers(id),
    pass_mark INT,
    full_mark INT,
    description TEXT,
    assignment_file VARCHAR(100)

);

错误：

column "course_id" referenced in foreign key constraint does not exist
SQL state: 42703

在课程和教师表的 ID 中插入数据后，我尝试运行第三个创建表代码，但没有变化。

Answer 1

你不能像那样引用一个列。首先，您必须添加想要创建外键的列，然后引用它。

create table courses(
id SERIAL PRIMARY KEY 
);
----------------------
create table teachers(
id SERIAL PRIMARY KEY 
);
----------------------

CREATE TABLE assignments(
    id SERIAL PRIMARY KEY ,
    given_date TIMESTAMP,
    deadline TIMESTAMP,
    course_id INT,
    teacher_id INT,
    pass_mark INT,
    full_mark INT,
    description TEXT,
    assignment_file VARCHAR(100),
    FOREIGN KEY(course_id) REFERENCES courses(id),
    FOREIGN KEY(teacher_id) REFERENCES teachers(id)

);