我刚开始使用mysqli\u multi\u查询，还没有花很多时间在php中。当我直接在db客户机（phpmyadmin）中应用sql时，它会成功，但它不会从php代码执行。此函数的返回是一个2项数组，其中填充了2条select语句的结果，但返回结果总是空的(注意：连接成功$con在别处有定义。）

function claimItem($key){
    //remove expiry, decrement quantity available, send Kate & Sasha an email.
    global $con;
    $sql = "SELECT A.name, B.name, C.quantity, B.id FROM invitees A, items B, invitees_items C WHERE C.activation_key = '$key' AND C.items_id = B.id AND C.invitees_id = A.id; SELECT @qnt := quantity, @itm := items_id FROM invitees_items WHERE `activation_key` = '$key'; UPDATE items SET num_available = GREATEST(num_available - @qnt, 0) WHERE id = @itm; UPDATE invitees_items SET expiry = null, activation_key = null WHERE activation_key = '$key';";
    $multiArr = array(array(), array());
    if (mysqli_multi_query($con,$sql)){
      $qcount = 0;
      do
        {
        // Store first result set
        $result=mysqli_store_result($con);
          // Fetch one and one row
          while ($row=mysqli_fetch_row($result))
            {
                array_push($multiArr[$qcount], $row);
            }
          // Free result set
          mysqli_free_result($result);
          $qcount++;
        }
      while (mysqli_next_result($con));
    }
    else {
        return "failure";
    }
    mysqli_close($con); 
    return $multiArr;
}