PHP develops simple book borrowing system complete book return function implementation code

Introduce the database file config.php

<?php include("config.php");?>

Create a complete return code file huanshu.php

<?php
require ('config.php');
//如果没有登录，退出
if ($_SESSION['id']==""){
   echo "<script language=javascript>alert('您还没有登陆');window.location='landing.php'</script>";
   exit();
}
$book_id=$_GET["book_id"];
//构建sql语句还书
//在lend表中删除该借书记录
$returnsql="DELETE FROM lend where book_id='$book_id' and user_id=".$_SESSION['id'];
mysqli_query($link,$returnsql) or die ("删除借书记录失败：".mysqli_errno($link));
//在book表中增加一本现存书数量
$booksql="UPDATE yx_books SET leave_number=leave_number+1 where id='$book_id'";
mysqli_query($link,$booksql) or die ("增加剩余书数量失败：".mysqli_error($link));
echo "<script language=javascript>alert('还书成功');window.location='index.php'</script>";
?>