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。
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)
);
