<?php
$id = $_GET['id']+0;
if($id==0) {
    echo "参数有误";
    exit;
}
$conn = mysql_connect('loaclhost','root','123456');
$sql = 'use msg';
mysql_query($sql,$conn);
$sql = "select * from denglu where id = $id";
$var = mysql_query($sql,$conn);
$msg = mysql_fetch_assoc($var);
if(!$msg) {
    echo '参数有误';
    exit;
}
print_r($msg);
?>

Notice: Undefined index: id in D:\server\apache\www\test.php on line 2
参数有误

http://localhost/test.php[color=#FF0000]?id=2[/color]

Warning: mysql_connect() [function.mysql-connect]: php_network_getaddresses: getaddrinfo failed: 不知道这样的主机。 in D:\server\apache\www\test.php on line 7

Warning: mysql_connect() [function.mysql-connect]: [2002] php_network_getaddresses: getaddrinfo failed: 不知道这样的主机。 (trying to connect via tcp://loaclhost:3306) in D:\server\apache\www\test.php on line 7

Warning: mysql_connect() [function.mysql-connect]: php_network_getaddresses: getaddrinfo failed: 不知道这样的主机。 in D:\server\apache\www\test.php on line 7

Warning: mysql_query() expects parameter 2 to be resource, boolean given in D:\server\apache\www\test.php on line 9

Warning: mysql_query() expects parameter 2 to be resource, boolean given in D:\server\apache\www\test.php on line 11

Warning: mysql_fetch_assoc() expects parameter 1 to be resource, null given in D:\server\apache\www\test.php on line 12
鍙傛暟鏈夎

$conn = mysql_connect('loaclhost','root','123456') or die("can not connect Mysql Server");
mysql_select_db("数据库名",$conn);//你的数据库名叫 use msg ？
$sql = "select * from denglu where id = $id";
$var = mysql_query($sql);

------解决方案--------------------
<?php
if(isset($_REQUEST['id'])){
	$id = $_REQUEST['id'];
	if($id == 0){
		exit("The parameter is wrong!");
	}
}
echo $id;
@ $conn = mysql_connect('localost', 'root', '123456') or die("Connection Failure:" .mysql_errno());
mysql_select_db('msg', $conn);
mysql_query("set names ''utf8");
$sql =  "select * from denglu where id = $id";
$result = mysql_query($sql);
while($rs = mysql_fetch_assoc($result)){
   var_dump($rs);
}
输入url: localhost/index.php?id=2即可获取到id

------解决方案--------------------
$id=isset($_GET["id"])?$_GET["id"]:0;