错误：mysqli_num_rows（）期望参数1为mysqli_result？

Question

所以，我得到了这个错误：     mysqli_num_rows（）期望参数1为mysqli_result

我的代码：

if(isset($_GET["email_pw"])) {

if($_GET["email_pw"]==$configs["email"]){
    $smarty->assign('message', 'Hoće li to majstore :)');           
} else {
$email_pw = stripslashes($_GET["email_pw"]);
$email_pw = mysqli_real_escape_string($connect, $email_pw);

$pw = mysqli_query($connect, 'SELECT * FROM clients WHERE email="'.$email_pw.'"');
$pw2 = mysqli_num_rows($pw); // ERROR LINE!!!!!!!!!!
if($pw2==1) {

function generatePassword($length=9, $strength=0) {
$vowels = 'aeuy';
$consonants = 'bdghjmnpqrstvz';
if ($strength & 1) {
    $consonants .= 'BDGHJLMNPQRSTVWXZ';
}
if ($strength & 2) {
    $vowels .= "AEUY";
}
if ($strength & 4) {
    $consonants .= '23456789';
}
if ($strength & 8) {
    $consonants .= '@#$%';
}

错误行是这样的：     $ pw2 = mysqli_num_rows（$ pw）;