CREATE TABLE courses (
course_id VARCHAR(10) PRIMARY KEY,
course_name VARCHAR(100) NOT NULL,
credits INT NOT NULL,
hours INT NOT NULL,
teacher_id VARCHAR(20) NOT NULL,
course_type ENUM('必修', '选修') NOT NULL,
description TEXT,
created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
FOREIGN KEY (teacher_id) REFERENCES users(user_id)
);