设计一个数据库应用系统：图书馆借还书系统。设计支撑这个应用的多个数据表，例如人员信息、图书信息、借还信息、收费信息等等。图书馆借还书系统：图书信息表支持购入同一个ISBN的书籍多本，支持按ISBN、图书名、出版社、作者、图书分类、出版年份进行书籍登记，可查询和删除（这是基本界面功能） 支持对内对外借阅；内部人员包括学生、学校职工；外部人员需登记身份证号、姓名等，需要押金；外部人员在借书数量限制2本；内部限制为5本；超期外部人员3元/天，内部1元/天，有超期的书籍，不让继续借新的。给出具体的sql和python源码

首先，我们需要设计以下数据表：

1. 人员信息表（person_info）：包含人员ID、姓名、身份证号、职业等字段。
2. 图书信息表（book_info）：包含书籍ID、书名、ISBN、作者、出版社、出版年份、图书分类、价格等字段。
3. 借还信息表（borrow_info）：包含借阅ID、人员ID、书籍ID、借阅时间、应还时间、实际归还时间、借阅状态等字段。
4. 收费信息表（fee_info）：包含收费ID、借阅ID、超期天数、应收费用、实际收费等字段。

接下来，我们可以使用以下 SQL 语句创建这些表：

-- 创建人员信息表
CREATE TABLE person_info (
    person_id INT PRIMARY KEY,
    name VARCHAR(50),
    id_card VARCHAR(50),
    profession VARCHAR(50)
);

-- 创建图书信息表
CREATE TABLE book_info (
    book_id INT PRIMARY KEY,
    book_name VARCHAR(50),
    isbn VARCHAR(50),
    author VARCHAR(50),
    publisher VARCHAR(50),
    publish_year INT,
    category VARCHAR(50),
    price FLOAT
);

-- 创建借还信息表
CREATE TABLE borrow_info (
    borrow_id INT PRIMARY KEY,
    person_id INT,
    book_id INT,
    borrow_time DATETIME,
    due_time DATETIME,
    return_time DATETIME,
    status INT,
    FOREIGN KEY (person_id) REFERENCES person_info(person_id),
    FOREIGN KEY (book_id) REFERENCES book_info(book_id)
);

-- 创建收费信息表
CREATE TABLE fee_info (
    fee_id INT PRIMARY KEY,
    borrow_id INT,
    overdue_days INT,
    due_fee FLOAT,
    actual_fee FLOAT,
    FOREIGN KEY (borrow_id) REFERENCES borrow_info(borrow_id)
);

接下来，我们可以使用 Python 编写一个简单的图书馆借还书系统。以下是一个基本的示例：

import sqlite3
from datetime import datetime, timedelta

# 连接到数据库
conn = sqlite3.connect('library.db')

# 获取游标
c = conn.cursor()

# 插入人员信息
c.execute("INSERT INTO person_info VALUES (1, '张三', '1234567890', '学生')")
c.execute("INSERT INTO person_info VALUES (2, '李四', '0987654321', '教师')")

# 插入图书信息
c.execute("INSERT INTO book_info VALUES (1, 'Python编程入门', '9787115461360', '乔伊斯', '人民邮电出版社', 2020, '计算机', 39.8)")
c.execute("INSERT INTO book_info VALUES (2, '深入浅出MySQL', '9787121317996', '周楷文', '电子工业出版社', 2019, '数据库', 49.8)")
c.execute("INSERT INTO book_info VALUES (3, 'Java核心技术', '9787111596669', 'Cay S. Horstmann', '机械工业出版社', 2019, '计算机', 119.0)")

# 提交更改
conn.commit()

# 从图书信息表中查询书籍信息
def search_book(query):
    c.execute("SELECT * FROM book_info WHERE book_name LIKE ? OR isbn LIKE ? OR author LIKE ? OR publisher LIKE ? OR category LIKE ? OR publish_year = ?", 
              ('%'+query+'%', '%'+query+'%', '%'+query+'%', '%'+query+'%', '%'+query+'%', query))
    books = c.fetchall()
    return books

# 借书
def borrow_book(person_id, book_id):
    # 查询人员信息
    c.execute("SELECT * FROM person_info WHERE person_id = ?", (person_id,))
    person = c.fetchone()
    # 查询书籍信息
    c.execute("SELECT * FROM book_info WHERE book_id = ?", (book_id,))
    book = c.fetchone()
    # 查询借阅信息
    c.execute("SELECT * FROM borrow_info WHERE person_id = ? AND book_id = ? AND status = 0", (person_id, book_id))
    borrow = c.fetchone()
    if person and book and not borrow:
        # 判断借书数量限制
        c.execute("SELECT COUNT(*) FROM borrow_info WHERE person_id = ? AND status = 0", (person_id,))
        count = c.fetchone()[0]
        if person[3] == '外部人员' and count >= 2:
            return '外部人员最多只能借阅2本书籍'
        elif person[3] == '内部人员' and count >= 5:
            return '内部人员最多只能借阅5本书籍'
        # 更新图书信息
        c.execute("UPDATE book_info SET stock = stock - 1 WHERE book_id = ?", (book_id,))
        # 插入借阅信息
        borrow_time = datetime.now()
        due_time = borrow_time + timedelta(days=30)
        c.execute("INSERT INTO borrow_info (person_id, book_id, borrow_time, due_time, status) VALUES (?, ?, ?, ?, 0)", 
                  (person_id, book_id, borrow_time, due_time))
        conn.commit()
        return '借阅成功'
    elif borrow:
        return '该图书已经被借阅'
    else:
        return '借阅失败'

# 还书
def return_book(person_id, book_id):
    # 查询借阅信息
    c.execute("SELECT * FROM borrow_info WHERE person_id = ? AND book_id = ? AND status = 0", (person_id, book_id))
    borrow = c.fetchone()
    if borrow:
        # 更新图书信息
        c.execute("UPDATE book_info SET stock = stock + 1 WHERE book_id = ?", (book_id,))
        # 更新借阅信息
        return_time = datetime.now()
        c.execute("UPDATE borrow_info SET return_time = ?, status = 1 WHERE borrow_id = ?", (return_time, borrow[0]))
        # 计算超期天数和费用
        due_time = borrow[4]
        overdue_days = (return_time - due_time).days
        if overdue_days > 0:
            due_fee = overdue_days * 3 if borrow[2] == '外部人员' else overdue_days
            c.execute("INSERT INTO fee_info (borrow_id, overdue_days, due_fee, actual_fee) VALUES (?, ?, ?, 0)", 
                      (borrow[0], overdue_days, due_fee))
        conn.commit()
        return '还书成功'
    else:
        return '还书失败'

# 关闭数据库连接
conn.close()

这个示例提供了几个基本功能，包括查询图书信息、借书、还书等。你可以根据实际需求进行修改和扩展。