无法在sql UPDATE语句

Question

第一页：

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<?php
session_start();

//db info

$conn = new mysqli("$server","$user_name","$password","$database");

$sql = "SELECT id FROM Client_Information order by id desc limit 1";
$result = $conn->query($sql);

if ($result->num_rows >0) {
	while($row = $result->fetch_assoc()) {
		$id=$row['id'] + 1;
	}
}

$_SESSION['id'] = $id;
$sitename = $_POST['sitename'];
$sitetype = $_POST['sitetype'];
$color1 = $_POST['color1'];
$color2 = $_POST['color2'];
$color3 = $_POST['color3'];
$color4 = $_POST['color4'];
$sitedescription = $_POST['sitedescription'];
$aboutme = $_POST['aboutme'];
$contactname = $_POST['contactname'];
$phone = $_POST['phone'];
$email = $_POST['email'];
$address = $_POST['address'];

if (isset($sitename) && isset($sitetype) && isset($color1) 
	&& isset($color2) && isset($contactname) && isset($phone) 
	&& isset($email) && isset($address) && isset($sitedescription) 
	&& isset($aboutme)) {	
	
	$sql = "INSERT INTO Client_Information (id, sitename, sitetype, color1, color2,
										color3, color4, sitedescription, aboutme, 
										contactname, phone, email, address, timestamp)
			VALUES ('$id', '$sitename', '$sitetype', '$color1', '$color2',
					'$color3', '$color4', '$sitedescription', '$aboutme', 
					'$contactname', '$phone', '$email', '$address', 
					CURRENT_TIMESTAMP)";
				
	$conn->query($sql);

	header('Location: images.php');
}



mysqli_close($conn);
?>

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第二页：

＆＃13;

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<?php
session_start();


echo $_SESSION['id'];

//db info

$conn = new mysqli("$server","$user_name","$password","$database");

if (!$conn) {
    die("Connection failed: " . mysqli_connect_error());
}

$wherevar = $_SESSION['id'];
$exsitename1 = $_POST['exsitename1'];
$exsitename2 = $_POST['exsitename2'];
$exsitename3 = $_POST['exsitename3'];
$exsitename4 = $_POST['exsitename4'];
$exsiteurl1 = $_POST['exsiteurl1'];
$exsiteurl2 = $_POST['exsiteurl2'];
$exsiteurl3 = $_POST['exsiteurl3'];
$exsiteurl4 = $_POST['exsiteurl4'];
$exsitedescr1 = $_POST['exsitedescr1'];
$exsitedescr2 = $_POST['exsitedescr2'];
$exsitedescr3 = $_POST['exsitedescr3'];
$exsitedescr4 = $_POST['exsitedescr4'];

if (isset($exsitename1) && isset($exsitename2) && isset($exsitename3) && isset($exsitename4)
	 && isset($exsiteurl1) && isset($exsiteurl2) && isset($exsiteurl3) && isset($exsiteurl4)
	 && isset($exsitedescr1) && isset($exsitedescr2) && isset($exsitedescr3) && isset($exsitedescr4)) {
	$sql =  "UPDATE Client_Information
			SET exsitename1='$exsitename1', exsitename2='$exsitename2', exsitename3='$exsitename3', 
				exsitename4='$exsitename4', exsiteurl1='$exsiteurl1', exsiteurl2='$exsiteurl2', 
				exsiteurl3='$exsiteurl3', exsiteurl4='$exsiteurl4',	exsitedescr1='$exsitedescr1', 
			 	exsitedescr2='$exsitedescr2', exsitedescr3='$exsitedescr3', exsitedescr4='$exsitedescr4'
			WHERE id = '$wherevar'";
	
	$conn->query($sql);
	
	header('Location: index.php');
}

session_destroy();
mysqli_close($conn);
?>

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因此第一页工作正常并将所有数据插入到数据库中，但是当第二页运行时，它不会更新在第一页上插入的同一行。它只留下所有这些变量。 在第二页上，我试图让它编辑刚刚创建的行。