运行代码报错

$con = mysql_connect('127.0.0.1', 'root', 'root') or die('数据库连接失败');

if (!$con){

 die('Could not connect: ' . mysql_error());

 }

$db_selected = mysql_select_db("test_db",$con);

mysql_query("set names 'utf8'");

$sql = "SELECT * from Person WHERE Lastname='Adams'";

$result = mysql_query($sql,$con);

print_r(mysql_fetch_assoc($result));

报错如下：

Warning: mysql_fetch_assoc() expects parameter 1 to be resource, boolean given in D:\phpStudy\WWW\test\test.php on line 11