写个学生管理系统，并用数据库存储数据

好的，以下是一个简单的学生管理系统的设计和实现过程：

1. 数据库设计

我们可以使用 MySQL 数据库来存储学生信息，首先需要设计数据库表，如下所示：

CREATE TABLE `students` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `name` varchar(50) NOT NULL,
  `age` int(11) NOT NULL,
  `gender` varchar(10) NOT NULL,
  `major` varchar(50) NOT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8mb4;

其中，`students` 表包含以下字段：

- `id`：学生编号，自增长整数类型；
- `name`：学生姓名，非空字符串类型；
- `age`：学生年龄，整数类型；
- `gender`：学生性别，非空字符串类型；
- `major`：学生专业，非空字符串类型。

2. 实现代码

接下来，我们可以使用 Python 语言和 MySQL 数据库连接器 pymysql 来实现学生管理系统。代码如下所示：

# -*- coding: utf-8 -*-
import pymysql

# 连接数据库
conn = pymysql.connect(
    host='localhost',
    port=3306,
    user='root',
    password='123456',
    db='test',
    charset='utf8mb4'
)

# 添加学生
def add_student(name, age, gender, major):
    try:
        with conn.cursor() as cursor:
            sql = "INSERT INTO students (name, age, gender, major) VALUES (%s, %s, %s, %s)"
            cursor.execute(sql, (name, age, gender, major))
        conn.commit()
        print("Add student success!")
    except Exception as e:
        conn.rollback()
        print("Add student failed:", e)

# 删除学生
def delete_student(id):
    try:
        with conn.cursor() as cursor:
            sql = "DELETE FROM students WHERE id=%s"
            cursor.execute(sql, (id,))
        conn.commit()
        print("Delete student success!")
    except Exception as e:
        conn.rollback()
        print("Delete student failed:", e)

# 修改学生
def update_student(id, name, age, gender, major):
    try:
        with conn.cursor() as cursor:
            sql = "UPDATE students SET name=%s, age=%s, gender=%s, major=%s WHERE id=%s"
            cursor.execute(sql, (name, age, gender, major, id))
        conn.commit()
        print("Update student success!")
    except Exception as e:
        conn.rollback()
        print("Update student failed:", e)

# 查询学生
def query_student(id):
    try:
        with conn.cursor() as cursor:
            sql = "SELECT * FROM students WHERE id=%s"
            cursor.execute(sql, (id,))
            result = cursor.fetchone()
            if result:
                print("ID\tName\tAge\tGender\tMajor")
                print("{0}\t{1}\t{2}\t{3}\t{4}".format(result[0], result[1], result[2], result[3], result[4]))
            else:
                print("No student found!")
    except Exception as e:
        print("Query student failed:", e)

# 显示全部学生
def show_students():
    try:
        with conn.cursor() as cursor:
            sql = "SELECT * FROM students"
            cursor.execute(sql)
            results = cursor.fetchall()
            if results:
                print("ID\tName\tAge\tGender\tMajor")
                for result in results:
                    print("{0}\t{1}\t{2}\t{3}\t{4}".format(result[0], result[1], result[2], result[3], result[4]))
            else:
                print("No student found!")
    except Exception as e:
        print("Show students failed:", e)

# 关闭数据库连接
def close_connection():
    conn.close()

# 测试代码
if __name__ == '__main__':
    add_student('Tom', 20, 'male', 'Computer Science')
    add_student('Lucy', 21, 'female', 'Mathematics')
    show_students()
    update_student(1, 'Jerry', 22, 'male', 'Physics')
    query_student(1)
    delete_student(2)
    show_students()
    close_connection()

在以上代码中，我们定义了以下函数：

- `add_student(name, age, gender, major)`：添加学生，参数为学生姓名、年龄、性别和专业；
- `delete_student(id)`：删除学生，参数为学生编号；
- `update_student(id, name, age, gender, major)`：修改学生，参数为学生编号、姓名、年龄、性别和专业；
- `query_student(id)`：查询学生，参数为学生编号；
- `show_students()`：显示全部学生；
- `close_connection()`：关闭数据库连接。

在测试代码中，我们先添加了两个学生，然后显示全部学生信息，接着修改了学生信息并查询学生，最后删除了一个学生并再次显示全部学生信息。

3. 运行结果

运行以上代码后，可以得到如下输出结果：

Add student success!
Add student success!
ID	Name	Age	Gender	Major
1	Tom	20	male	Computer Science
2	Lucy	21	female	Mathematics
Update student success!
ID	Name	Age	Gender	Major
1	Jerry	22	male	Physics
Delete student success!
ID	Name	Age	Gender	Major
1	Jerry	22	male	Physics

以上就是一个简单的学生管理系统的设计和实现过程。