使用php（mysqli）连续调用mysql过程不会产生结果

以下是我的存储过程：

CREATE PROCEDURE productFromCatID(
  IN ID INT
)
BEGIN
  SELECT * FROM product
  WHERE cat_id = ID;
END;

这是我的php文件：

try {
  $mysqli = new mysqli($db_host, $db_username, $db_password, $db_name);
  $con = new mysqli($db_host, $db_username, $db_password, $db_name);
} catch (PDOException $exception) {
  echo "Connection error: " . $exception->getMessage();
}

print '<h3>MYSQLI: simple select</h3>';
$rs = $mysqli->query( 'SELECT * FROM product WHERE cat_id =2;' );
while($row = $rs->fetch_object())
{
  print_r($row);
}

$q = 'CALL productFromCatID(1)';
$rs = $mysqli->query( $q );
print '<h3>MYSQLI: '.$q.'</h3>';
while($row = $rs->fetch_object())
{
  print_r($row);
}

$q = 'CALL productFromCatID(2)';
$rs = $mysqli->query( $q );
print '<h3>MYSQLI: '.$q.'</h3>';
while($row = $rs->fetch_object())
{
  print_r($row);
}

正如您在底部看到的，我在第39行得到了一个错误，在最后一次调用productFromCatID之后，它处于while循环的状态

while($row = $rs->fetch_object())

那么，我在调用程序时是否做错了什么，或者我是否错过了一个步骤

$q = 'CALL productFromCatID(1)';
$rs = $mysqli->query( $q );
print '<h3>MYSQLI: '.$q.'</h3>';
while($row = $rs->fetch_object())
{
  print_r($row);
}

然后可以执行下一个过程调用

while($row = $rs->fetch_object())

$q = 'CALL productFromCatID(1)';
$rs = $mysqli->query( $q );
print '<h3>MYSQLI: '.$q.'</h3>';
while($row = $rs->fetch_object())
{
  print_r($row);
}

while ($mysqli->next_result()) {
    $rs = $mysqli->use_result();
    if ($rs instanceof mysqli_result) {
        $rs->free();
    }
}