请问这两行代码有什么区别？我试了一下都可以运行成功。
$query = "insert into books values (' ".$isbn." ', ' ".$author." ', ' ".$title." ', ' ".$price." ')";
$query = "insert into books values (' $isbn ', ' $author ', ' $title', ' $price ')";`
完整代码from PHP和MySQL Web开发(原书第4版)：
<html>
<head>
<title>TODO supply a title</title>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
</head>
<body>
<h1>Book-O-Rama Book Entry Result</h1>
<?php
//create short variable names
$isbn=$_POST['isbn'];
$author=$_POST['author'];
$title=$_POST['title'];
$price=$_POST['price'];
if (!$isbn || !$author || !$title || !$price){
echo "You have not entered all the required details. <br />". "Please go back and try again";
exit;
}
if (!get_magic_quotes_gpc()){
$isbn = addslashes($isbn);
$author = addslashes($author);
$title = addslashes($title);
$price = doubleval($price);
}
@ $db = new mysqli('localhost', 'root', '123', 'mydb');
if (mysqli_connect_errno()){
echo "Error: Could not connect to database. Please try again later.";
exit;
}
$query = "insert into books values (' ".$isbn." ', ' ".$author." ', ' ".$title." ', ' ".$price." ')";
$result = $db->query($query);
if ($result) {
echo $db->affected_rows. "book inserted into database.";
} else {
echo "An error has occurred. The item was not added.";
}
$db->close();
?>
</body>
</html>
