当我尝试将旧的sql切换到sqli时，有人可以告诉我为什么这不起作用：

$query = "SELECT * FROM `product_category`";
$result = mysql_query($query, $connect) or die("could not perform query: " . mysql_error());
$num_rows = mysql_num_rows($result);

for ($i=0; $i < $num_rows; $i++)
{
    $ID = mysql_result($result,$i,"ID");
    $name = mysql_result($result,$i,"name");
    $description = mysql_result($result,$i,"description");

至：

$query = ("SELECT * FROM `product_category`");
$result = mysqli_query($connect, $query) or die("could not perform query");
$num_rows = mysqli_num_rows($result);

for ($i=0; $i < $num_rows; $i++)
{
    $ID = mysqli_result($result, "ID");
    $name = mysqli_result($result,$i,"name");
    $description = mysqli_result($result,$i,"description");`

它一直给我一个错误：“致命错误：调用未定义函数mysqli_result（）”