学生表的DDL和DML

 DDL

-- 创建学生表
CREATE TABLE students (student_id INT PRIMARY KEY AUTO_INCREMENT,studentname VARCHAR(50),age INT,gender VARCHAR(10)
);-- 创建课程表
CREATE TABLE courses (course_id INT PRIMARY KEY AUTO_INCREMENT,course_name VARCHAR(50)
);-- 创建教师表
CREATE TABLE teachers (teacher_id INT PRIMARY KEY AUTO_INCREMENT,teachername VARCHAR(50),department VARCHAR(50)
);-- 创建成绩表
CREATE TABLE grades (grade_id INT PRIMARY KEY AUTO_INCREMENT,student_id INT,course_id INT,grade DECIMAL(5, 2),FOREIGN KEY (student_id) REFERENCES students(student_id),FOREIGN KEY (course_id) REFERENCES courses(course_id)
);-- 创建授课表
CREATE TABLE teachings (teaching_id INT PRIMARY KEY AUTO_INCREMENT,teacher_id INT,course_id INT,FOREIGN KEY (teacher_id) REFERENCES teachers(teacher_id),FOREIGN KEY (course_id) REFERENCES courses(course_id)
);

DML

-- 插入学生数据
INSERT INTO students (name, age, gender)
VALUES ('张三', 18, '男'),('李四', 19, '女'),('王五', 20, '男');-- 插入课程数据
INSERT INTO courses (course_name)
VALUES ('数学'),('英语'),('物理');-- 插入教师数据
INSERT INTO teachers (name, department)
VALUES ('赵老师', '数学系'),('钱老师', '英语系'),('孙老师', '物理系');-- 插入成绩数据
INSERT INTO grades (student_id, course_id, grade)
VALUES (1, 1, 85.5),(1, 2, 78.0),(2, 1, 90.0),(2, 2, 88.5),(3, 1, 75.0),(3, 3, 80.0);-- 插入授课数据
INSERT INTO teachings (teacher_id, course_id)
VALUES (1, 1),(2, 2),(3, 3);