作为新手，只能一次次的请你们帮助我了

这只是一部分代码：
$conn=new mysqli('127.0.0.1','root','123456','zichao1');
$query="select * from regist where UserName='$UserName1'";
$result=mysqli_query($conn,$query);
$row=mysql_fetch_array($result);
while ($row)
{
if ($row["UserName"]==$UserName1)
{
$error=true;
echo "用户名已存在<br>";
}
}
预览之后出现了：
Warning: mysql_fetch_array() expects parameter 1 to be resource, boolean given in D:\server\Apache24\htdocs\add.php on line 105
Please help