mysqli_fetch_array() expects parameter 1 tobe mysqli_result bool given in31

    $strSPQuery = "SELECT * FROM `san_pham` where ma_san_pham=".$arrMa[$i];
    $resultSp= mysqli_query($conn,$strSPQuery);
    $rowsp = mysqli_fetch_array($resultSp);
    $tong +=  $rowsp["gia"]*$arrSl[$i];