UML 类图

-- 示例：学生选课系统
CREATE TABLE student (
  id BIGINT NOT NULL AUTO_INCREMENT COMMENT '学生ID',
  student_no VARCHAR(20) NOT NULL COMMENT '学号',
  name VARCHAR(50) NOT NULL COMMENT '姓名',
  class_name VARCHAR(100) COMMENT '班级',
  PRIMARY KEY (id),
  UNIQUE KEY uk_student_no (student_no)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COMMENT='学生表';

CREATE TABLE course (
  id BIGINT NOT NULL AUTO_INCREMENT COMMENT '课程ID',
  code VARCHAR(20) NOT NULL COMMENT '课程编号',
  title VARCHAR(100) NOT NULL COMMENT '课程名称',
  credit DECIMAL(3,1) DEFAULT 0 COMMENT '学分',
  PRIMARY KEY (id),
  UNIQUE KEY uk_course_code (code)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COMMENT='课程表';

CREATE TABLE enrollment (
  id BIGINT NOT NULL AUTO_INCREMENT COMMENT '选课ID',
  student_id BIGINT NOT NULL COMMENT '学生ID',
  course_id BIGINT NOT NULL COMMENT '课程ID',
  score DECIMAL(5,2) COMMENT '成绩',
  PRIMARY KEY (id),
  UNIQUE KEY uk_student_course (student_id, course_id),
  FOREIGN KEY (student_id) REFERENCES student(id),
  FOREIGN KEY (course_id) REFERENCES course(id)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COMMENT='选课记录表';