<?PHP
$conn=mysqli_connect("localhost", "-", "-", "-");
$password=password_hash($_POST['jelszo'], PASSWORD_BCRYPT, ["cost" => 14]);
$rownum=mysqli_num_rows(mysqli_query($conn, "SELECT id FROM users WHERE password='".$password."'"));
while($rownum==1)
{
    $password=password_hash($_POST['jelszo'], PASSWORD_BCRYPT, ["cost" => 14]);
    $rownum=mysqli_num_rows(mysqli_query($conn, "SELECT id FROM users WHERE password='".$password."'"));
}