通过PHP / MySQL搜索联合表获取正确的数组键

I have two tables:

1st table (t1):

item_no | item_desc
-------------
200  | d1  
250  | d2 
257  | d3 
305  | d4  
605  | d5
606  | d6 

2nd table (t2)

id | item_no | item_value
-------------
1 | 200  | v1_200  
1 | 250  | v1_250 
1 | 257  | v1_257 
1 | 305  | v1_305
1 | 605  | v1_605  
1 | 606  | v1_606
2 | 200  | v2_200  
2 | 250  | v2_250 
2 | 257  | v2_257 
2 | 305  | v2_305  
2 | 606  | v2_606

I get the value of the id field in t2 via $id= $_POST['id']; and do the security checks on it, etc.

I perform a join search of both tables with a query like this:

$items= array();
$items_no = array('200', '250', '257', '305', '605', '606');
$items_nos = implode(",", $nutrient_no);

$sql = "SELECT item_value FROM t1 join t2 ON  t1.item_no=t2.item_no WHERE t1.id='$id' AND t2.item_no in ($items_nos)"; 

Finally, I extract the results like this:

$retval = mysql_query($sql) or die('Query failed: ' . mysql_error());
while($row = mysql_fetch_assoc($retval))
{
$item_value[] = $row['item_value'];
$first_item = $item_value['0'];
$second_item = $item_value['1'];
....
$last_item = $item_value['5'];    
}

Problem is, for searches on id # 2, as illustrated in the example I gave above, item_no 605 does not exist. The search still works fine, but the array keys are no longer right, i.e. $last_item's value is not returned properly because the key is now 4 instead of 5.

IMPORTANT: depending on the id used in search, none, one or more rows may be missing in the results.

I have tried this as a solution:

$items_count = count($item_value);
for( $x = 1; $x <= $items_count ; $x++ ) {
$foo = 'item_value' . $x;
if ( isset( $$item_value[$x-1])) {
    $$foo = $$item_value[$x-1];
}
else {
    $$foo = '';
}
$last_item = $foo['5']; 
}

but it doesn't seem to work.

What am I doing wrong? Is there a better way to do this? Any help greatly appreciated!

It's strange to me to have a variable number of variables depending on a query result... but you could try something like that:

for ($i=0; $i < count($arr)-1; $i++) { 
    ${"item_n" . $i} = $arr[$i];
}

And for the last item:

$last_item = end(array_values($arr));