sql图书管理系统多表查询casec使用

SQL图书管理系统中的多表查询通常涉及在数据库的不同表格之间关联数据，以便获取所需的信息。CASE WHEN语句在这里可以用于条件筛选和结果的定制。CASEC可能是某个特定情况下的缩写，这里假设它代表"Case Expression with Conditions"。

例如，如果你有一个包含书籍信息的`books`表和一个包含作者信息的`authors`表，你想查询每个书籍的标题、作者名以及是否为畅销书（基于销售量），你可以这样做：

SELECT 
    books.title,
    authors.name AS author_name,
    CASE 
        WHEN books.sales_volume > 100 THEN '畅销'
        ELSE '非畅销'
    END AS book_status
FROM 
    books
JOIN 
    authors ON books.author_id = authors.id;

在这个查询中，CASE WHEN判断了书籍的销售量是否大于100，如果是，则将`book_status`标记为'畅销'，否则为'非畅销'。通过JOIN操作，我们能够从两个表中合并数据。

相关问题

用javaweb写图书管理系统

好的，下面是一个简单的图书管理系统的示例，使用Java Web技术实现。

1. 数据库设计

首先，我们需要设计数据库来存储图书信息。我们可以创建一个名为“library”的数据库，并在其中创建一个名为“books”的表来存储图书信息。该表包含以下字段：

id: 图书ID（自增长）
title: 图书标题
author: 作者
publisher: 出版社
price: 价格

2. 创建Java Web项目

接下来，我们需要创建一个Java Web项目。您可以使用Eclipse等IDE，或者手动创建项目文件夹和文件。

3. 创建实体类

我们需要创建一个Java类来表示图书对象。这个类应该包含与数据库表中的字段相对应的属性，以及getter和setter方法。

public class Book {
    private int id;
    private String title;
    private String author;
    private String publisher;
    private double price;

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getTitle() {
        return title;
    }

    public void setTitle(String title) {
        this.title = title;
    }

    public String getAuthor() {
        return author;
    }

    public void setAuthor(String author) {
        this.author = author;
    }

    public String getPublisher() {
        return publisher;
    }

    public void setPublisher(String publisher) {
        this.publisher = publisher;
    }

    public double getPrice() {
        return price;
    }

    public void setPrice(double price) {
        this.price = price;
    }
}

4. 创建DAO类

我们需要创建一个DAO（数据访问对象）类，用于连接数据库并实现与图书相关的操作（如添加、删除、更新、查询等）。下面是一个简单的示例：

public class BookDAO {
    private Connection conn;

    public BookDAO() {
        try {
            Class.forName("com.mysql.jdbc.Driver");
            String url = "jdbc:mysql://localhost:3306/library";
            String user = "root";
            String password = "123456";
            conn = DriverManager.getConnection(url, user, password);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    public List<Book> getAllBooks() {
        List<Book> books = new ArrayList<Book>();
        try {
            Statement stmt = conn.createStatement();
            String sql = "SELECT * FROM books";
            ResultSet rs = stmt.executeQuery(sql);
            while (rs.next()) {
                Book book = new Book();
                book.setId(rs.getInt("id"));
                book.setTitle(rs.getString("title"));
                book.setAuthor(rs.getString("author"));
                book.setPublisher(rs.getString("publisher"));
                book.setPrice(rs.getDouble("price"));
                books.add(book);
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
        return books;
    }

    public void addBook(Book book) {
        try {
            PreparedStatement stmt = conn.prepareStatement("INSERT INTO books(title, author, publisher, price) VALUES (?, ?, ?, ?)");
            stmt.setString(1, book.getTitle());
            stmt.setString(2, book.getAuthor());
            stmt.setString(3, book.getPublisher());
            stmt.setDouble(4, book.getPrice());
            stmt.executeUpdate();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    public void deleteBook(int id) {
        try {
            PreparedStatement stmt = conn.prepareStatement("DELETE FROM books WHERE id = ?");
            stmt.setInt(1, id);
            stmt.executeUpdate();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    public void updateBook(Book book) {
        try {
            PreparedStatement stmt = conn.prepareStatement("UPDATE books SET title = ?, author = ?, publisher = ?, price = ? WHERE id = ?");
            stmt.setString(1, book.getTitle());
            stmt.setString(2, book.getAuthor());
            stmt.setString(3, book.getPublisher());
            stmt.setDouble(4, book.getPrice());
            stmt.setInt(5, book.getId());
            stmt.executeUpdate();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    public Book getBookById(int id) {
        Book book = null;
        try {
            PreparedStatement stmt = conn.prepareStatement("SELECT * FROM books WHERE id = ?");
            stmt.setInt(1, id);
            ResultSet rs = stmt.executeQuery();
            if (rs.next()) {
                book = new Book();
                book.setId(rs.getInt("id"));
                book.setTitle(rs.getString("title"));
                book.setAuthor(rs.getString("author"));
                book.setPublisher(rs.getString("publisher"));
                book.setPrice(rs.getDouble("price"));
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
        return book;
    }
}

5. 创建Servlet类

我们需要创建一个Servlet类来处理HTTP请求，并将请求转发到相应的JSP页面。下面是一个简单的示例：

public class BookServlet extends HttpServlet {
    private BookDAO bookDAO = new BookDAO();

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String action = request.getServletPath();
        switch (action) {
            case "/new":
                showNewForm(request, response);
                break;
            case "/insert":
                insertBook(request, response);
                break;
            case "/delete":
                deleteBook(request, response);
                break;
            case "/edit":
                showEditForm(request, response);
                break;
            case "/update":
                updateBook(request, response);
                break;
            default:
                listBooks(request, response);
                break;
        }
    }

    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doGet(request, response);
    }

    private void listBooks(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        List<Book> books = bookDAO.getAllBooks();
        request.setAttribute("books", books);
        RequestDispatcher dispatcher = request.getRequestDispatcher("book-list.jsp");
        dispatcher.forward(request, response);
    }

    private void showNewForm(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        RequestDispatcher dispatcher = request.getRequestDispatcher("book-form.jsp");
        dispatcher.forward(request, response);
    }

    private void insertBook(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String title = request.getParameter("title");
        String author = request.getParameter("author");
        String publisher = request.getParameter("publisher");
        double price = Double.parseDouble(request.getParameter("price"));
        Book book = new Book();
        book.setTitle(title);
        book.setAuthor(author);
        book.setPublisher(publisher);
        book.setPrice(price);
        bookDAO.addBook(book);
        response.sendRedirect("list");
    }

    private void deleteBook(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        int id = Integer.parseInt(request.getParameter("id"));
        bookDAO.deleteBook(id);
        response.sendRedirect("list");
    }

    private void showEditForm(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        int id = Integer.parseInt(request.getParameter("id"));
        Book book = bookDAO.getBookById(id);
        request.setAttribute("book", book);
        RequestDispatcher dispatcher = request.getRequestDispatcher("book-form.jsp");
        dispatcher.forward(request, response);
    }

    private void updateBook(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        int id = Integer.parseInt(request.getParameter("id"));
        String title = request.getParameter("title");
        String author = request.getParameter("author");
        String publisher = request.getParameter("publisher");
        double price = Double.parseDouble(request.getParameter("price"));
        Book book = new Book();
        book.setId(id);
        book.setTitle(title);
        book.setAuthor(author);
        book.setPublisher(publisher);
        book.setPrice(price);
        bookDAO.updateBook(book);
        response.sendRedirect("list");
    }
}

6. 创建JSP页面

最后，我们需要创建JSP页面来显示图书信息和处理用户输入。下面是一个简单的示例：

book-list.jsp

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>图书列表</title>
</head>
<body>
    <h1>图书列表</h1>
    <table border="1">
        <tr>
            <th>ID</th>
            <th>标题</th>
            <th>作者</th>
            <th>出版社</th>
            <th>价格</th>
            <th>操作</th>
        </tr>
        <c:forEach var="book" items="${books}">
            <tr>
                <td>${book.id}</td>
                <td>${book.title}</td>
                <td>${book.author}</td>
                <td>${book.publisher}</td>
                <td>${book.price}</td>
                <td>
                    <a href="edit?id=${book.id}">编辑</a>
                    <a href="delete?id=${book.id}" onclick="return confirm('确定要删除该图书吗？')">删除</a>
                </td>
            </tr>
        </c:forEach>
    </table>
    <br>
    <a href="new">添加图书</a>
</body>
</html>

book-form.jsp

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>图书管理</title>
</head>
<body>
    <h1>图书管理</h1>
    <form action="${action}" method="post">
        <input type="hidden" name="id" value="${book.id}" />
        <label>标题：</label>
        <input type="text" name="title" value="${book.title}" /><br>
        <label>作者：</label>
        <input type="text" name="author" value="${book.author}" /><br>
        <label>出版社：</label>
        <input type="text" name="publisher" value="${book.publisher}" /><br>
        <label>价格：</label>
        <input type="text" name="price" value="${book.price}" /><br>
        <input type="submit" value="保存" />
    </form>
    <br>
    <a href="list">返回</a>
</body>
</html>

7. 配置Web.xml

最后，我们需要在Web.xml文件中配置Servlet。下面是一个简单的示例：

<servlet>
    <servlet-name>BookServlet</servlet-name>
    <servlet-class>com.example.BookServlet</servlet-class>
</servlet>

<servlet-mapping>
    <servlet-name>BookServlet</servlet-name>
    <url-pattern>/</url-pattern>
</servlet-mapping>

现在，您可以在浏览器中打开http://localhost:8080/来访问该图书管理系统，并进行添加、删除、更新和查询等操作。