实例
例子 1
使用如下 SELECT 语句：

SELECT DATEDIFF('2008-12-30','2008-12-29') AS DiffDate结果：

DiffDate
1

例子 2
使用如下 SELECT 语句：

SELECT DATEDIFF('2008-12-29','2008-12-30') AS DiffDate结果：

DiffDate
-1

function date_diff($start_date, $end_date, $returntype="d")
{
if ($returntype == "s")
$calc = 1;
if ($returntype == "m")
$calc = 60;
if ($returntype == "h")
$calc = (60*60);
if ($returntype == "d")
$calc = (60*60*24);

$_d1 = explode("-", $start_date);
$y1 = $_d1[0];
$m1 = $_d1[1];
$d1 = $_d1[2];

$_d2 = explode("-", $end_date);
$y2 = $_d2[0];
$m2 = $_d2[1];
$d2 = $_d2[2];

if (($y1 < 1970 || $y1 > 2037) || ($y2 < 1970 || $y2 > 2037))
{
return 0;
} else
{
$today_stamp = mktime(0,0,0,$m1,$d1,$y1);
$end_date_stamp = mktime(0,0,0,$m2,$d2,$y2);
$difference = round(($end_date_stamp-$today_stamp)/$calc);
return $difference;
}
}

$PassDate = date_diff($BugInfo[$_GET["BugID"]]["ClosedDate"],date('Y-m-d'), "d");