//fromDate
20140122
//toDate
20140220
//$arr
Array
(
    [0] => Array
        (
            [ISO_DATE] => 20140218
            [DAY_SUM_AMOUNT] => 3000
            [DAY_SUM_VOLUME] => 2
            [CONVERSION_PCT] => 100
        )

    [1] => Array
        (
            [ISO_DATE] => 20140219
            [DAY_SUM_AMOUNT] => 4000
            [DAY_SUM_VOLUME] => 1
            [CONVERSION_PCT] => 100
        )

)

//codetime

function createDateRangeArray($strDateFrom,$strDateTo) {
    $aryRange=array();
    $iDateFrom=mktime(1,0,0,substr($strDateFrom,5,2),     substr($strDateFrom,8,2),substr($strDateFrom,0,4));
    $iDateTo=mktime(1,0,0,substr($strDateTo,5,2),     substr($strDateTo,8,2),substr($strDateTo,0,4));
    if ($iDateTo>=$iDateFrom) {
        array_push($aryRange,date(‘Y-m-d’,$iDateFrom)); // first entry
        while ($iDateFrom<$iDateTo) {
            $iDateFrom+=86400; // add 24 hours
            array_push($aryRange,date(‘Y-m-d’,$iDateFrom));
        }
    }
    return $aryRange;
}
function recursive_array_search($needle,$haystack) {
    foreach($haystack as $key=>$value) {
        $current_key=$key;
        if($needle===$value OR (is_array($value) && recursive_array_search($needle,$value) !== false)) {
            return $current_key;
        }
    }
    return false;
}

$dates = createDateRangeArray($fromDate, $toDate);
$arr2 = array();
foreach($dates as $date) {
    $inArr = recursive_array_search($date, $arr);
    if($inArr!==false) {
        array_push($arr2, $arr[$inArr]);
    } else {
        array_push($arr2, array("ISO_DATE"=>$date, "DAY_SUM_AMOUNT"=>0, "DAY_SUM_VOLUME"=>0, "CONVERSION_PCT"=>0));
    }
}
$arr = $arr2;