数组用下标回重组数组，为什么重组出来的数组下标一直是第一个

数组用下标来重组数组，为什么重组出来的数组下标一直是第一个?

$id = array(8,31,32);

$resarr = array();
foreach($id as $num)
{
	$product = array(
					array(
						'pid'=>'10', 
						'name'=>'产品1'
						),
					array(
						'pid'=>'11', 
						'name'=>'产品2'
						)
					);
	foreach($product as $key => $value)
	{
		$result_value = "";
		foreach($value as $k => $v)
		{
			$result_value .= $result_value ? "|" : "";
			$result_value .=  $v['pid'];
		}
		$product[$key]['value'] = $result_value;
	}
	$resarr[$num] = $product;
	var_dump($resarr);
	echo "
";
}

$id = array(8,31,32);

$resarr = array();
foreach($id as $num)
{
	$product = array(
					array(
						'pid'=>'10', 
						'name'=>'产品1'
						),
					array(
						'pid'=>'11', 
						'name'=>'产品2'
						)
					);
	foreach($product as $key => $value)
	{
		$result_value = "";
		foreach($value as $k => $v)
		{
			$result_value .= $result_value ? "
------解决方案--------------------
" : "";
			$result_value .=  $v['pid'];
		}
		$product[$key]['value'] = $result_value;
	}
	$resarr[$num] = $product;
	
}
var_dump($resarr);
echo "
";