สอบถามการใช้ mysqli_num_rows กับ oop เพื่อเรียกนับค่า data มาแสดง

$sql = mysqli_query($con," sql ");

$num = mysqli_num_rows($sql);
$num data = 10 แถว

while($db = mysqli_fetch_array($sql ){
 data = 10
}

$sql= $Class->selectField("sql");

public function selectField($value){
		$sql = $this->con->query($value);
		$ResultSelect = array();
		while($rs = $sql->fetch_array()){
			array_push($ResultSelect,$rs);	
		}
		return $ResultSelect;
		$this->Closedb();
	}