Mysqli num_rows总是返回零

Question

Mysqli is exhibiting a strange behavior. For any queries that I try the num_rows is always 0.

        $email = trim(mysqli_real_escape_string($con1,$_POST['email']));
        $pwd = trim(mysqli_real_escape_string($con1, $_POST['pwd']));
        $result = $con1->prepare("select login.email,login.pwd from login 
                  where email = ?");
        if(!$result)
        {
            echo("error");
        }

        $result->bind_param('s',$email);
        $result->execute();
        print_r($result); //num_rows is zero
        if($result->num_rows > 0)
        {
            $result->bind_result($email1,$pwd1);
            $result->store_result();
            while($result->fetch())
            {
                echo("Email: ".$email1);

            }
        }

Answer 1

Try this :

$email = trim(mysqli_real_escape_string($con1,$_POST['email']));
$pwd = trim(mysqli_real_escape_string($con1, $_POST['pwd']));
$result = $con1->prepare("select login.email,login.pwd from login 
          where email = ?");
if(!$result)
{
    echo("error");
}
$result->bind_param('s',$email);
$result->execute();
$num_row = $result->num_rows;
print_r($num_row); //num_rows is zero
if($num_row > 0)
{
    $result->bind_result($email1,$pwd1);
    $result->store_result();
    while($result->fetch())
    {
        echo("Email: ".$email1);
    }
}