来自php数组的未定义索引错误

Question

我正在查询数据库，如下所示：

$result=mysql_query("SELECT name,items FROM mytable WHERE price='$price'");

现在，我想创建一个数组来插入作为此查询结果的值，例如假设这是结果数据：

 name    sellerid   quantity
 john       12     10
 joel       23     20
 brian      40     10

我已经将此数据插入到数组中并想要对其进行操作。（这是一个交易平台），假设用户想从数组中的数据中购买 25 件商品，因此要实现此脚本必须从 john 中取出 10 个项目，从 joel 中取出 15 个项目（加起来为 25），然后将它们的项目设置为剩余值，即 john's items=0 和 joel's items=5。

这是代码。我在这一行收到关于未定义索引的错误

$assignedQuantityPerUser[ $row[ "sellerid" ] ] += $totalUnitsOrdered;

这是代码的其余部分：

 $query="SELECT itemquantity,sellerid FROM mytable WHERE price='$price'";                     
//it is a table containing data about people selling their commoditities and the            program matches buyers and sellers by price
$foundItems = array();

// likely to be a parameter of a function...
$totalUnitsOrdered = 25;

// maps user to amount assigned from him
$assignedQuantityPerUser = array();


while ( $row = mysql_fetch_assoc( $cursor ) ) {

 // Still order Quantity left?
if ( 0 < $totalUnitsOrdered ) {

  if ( $row[ "itemquantity" ] <= $totalUnitsOrdered ) {

 // assign all of $row[ "items" ]
 $totalUnitsOrdered                         -= 0 + $row[ "itemquantity" ];
  $assignedQuantityPerUser[ $row[ "sellerid" ] ] += 0 + $row[ "itemquantity" ];
**//this is where in getting an error:r[ $row[ "sellerid" ]  is an undefined index**
}  else {

  // assign all the rest: $totalUnitsOrdered
  $totalUnitsOrdered                          = 0;
  $assignedQuantityPerUser[ $row[ "sellerid" ] ] += $totalUnitsOrdered;

}

 }


$newItem[] = $row[ "sellerid" ];
$newItem[] = $row[ "itemquantity" ];

// Append $newItem to the end of $foundItems 
 $foundItems[] = $newItem;

} // while

请协助。谢谢。

Answer 1

在使用之前初始化值：

if (!isset($assignedQuantityPerUser[$row["sellerid"]])) {
  $assignedQuantityPerUser[$row["sellerid"]] = 0;
}
$assignedQuantityPerUser[$row["sellerid"]] += $totalUnitsOrdered;