Get 30 days back date along with time

You can also use the DateTime class's sub() method together with an DateInterval:

$now = new DateTime();
$back = $now->sub(DateInterval::createFromDateString('30 days'));
echo $back->format('y-m-d g:i');

The problem is likely caused by the malformed date() call. The first argument passed to date() should be the format (as shown in the Docs) and the second should be an optional timestamp.

Try this:

$d2 = date('c', strtotime('-30 days'));

PHPFiddle

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As a short aside, the whole snippet can be simplified as follows:

$url = $row["url"];
$pageid = getPageID($url);
$date = date('y-m-d g:i');
$d1 = time();
$d2 = date('y-m-d g:i', strtotime('-30 days'));