PHP链接MySQL数据库

<?php
$conn = @mysql_connect("localhost", "-u", "-p") or die("数据库链接错误");
mysql_select_db("数据库名", $conn);
mysql_query("set names 'UTF8'");
?>

<?php
include("connection.php");
$username=$_COOKIE['username'];
$sql="select * from message where user='$username'";
$query=mysql_query($sql);
while($row=mysql_fetch_array($query)){}
?>

<?php
include("connection.php");
if(isset($_POST['submit']))
{
$sql="insert into message(id,user,title,content,lastdate) values('','$_COOKIE[username]','$_POST[title]','$_POST[content]',now())";
mysql_query($sql);
if(mysql_affected_rows($conn))
echo "<script>alert('插入成功！');</script>";
else
echo "<script>alert('插入失败！');</script>";
}
?>

<?php
include("connection.php");
if(isset($_POST['tid']))
{

$delete_sql = "delete from message where id =$_POST[tid]";
mysql_query($delete_sql);
if(mysql_affected_rows($conn))
echo "<script>alert('删除成功！'););location.href='listone.php';</script>";
else
echo "<script>alert('删除失败！'););location.href='listone.php';</script>";

}
?>

<?php
include("connection.php");
if(isset($_POST['submit']))
{
$sql="update message set title='$_POST[title]',content='$_POST[content]',lastdate=now() where id =$_POST[tid]";
mysql_query($sql);
if(mysql_affected_rows($conn))
echo "<script>alert('更新成功!');</script>";
else
echo "<script>alert('更新失败！');</script>";
}
?>