簡単ですがマンモス君に載ってないようなので…
スクリプト
$c = new Criteria();
$c->add(ReservePeer::TYPE, $reserve_type);
$c->add(ReservePeer::RESERVE_GROUP_ID, $reserve_group_id);
$c->addSelectColumn('MIN('.ReservePeer::MINUTES_PER_UNIT.')');
$c->addGroupByColumn(ReservePeer::TYPE);
$c->addGroupByColumn(ReservePeer::RESERVE_GROUP_ID);
$rs = ReservePeer::doSelectRS($c);
while ($rs->next())
{
$minutes_per_unit = $rs->getInt(1);
}

