Convert dates (Y-m-d) to Unix time code in an array

Using the code below, I get $row['dag_bev1'] and $row['dag_bev2'] as dates (Y-m-d), e g 2009-04-15. Need to convert to Unix time code. How could that be done?

unset ($events); 
$SQL = " SELECT * FROM medlem ";
$retid = mysql_db_query($db, $SQL, $cid);
if (!$retid) { echo( mysql_error()); }
else {
while ($row = mysql_fetch_array($retid)) {
$events1[]=$row['dag_bev1'];
$events2[]=$row['dag_bev2'];
}}
$events = array_merge($events1, $events2);

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