$sql=qq{SELECT SUM(?) AS `SUM` FROM ? WHERE `stationid`=? AND `datetime` >= "? ?" AND LEFT(`datetime`,10) <= "? ?" AND `sensid`=?};
$sth = $dbh->prepare( $sql );
$sth->execute($dbColName, $table, $stationId, $midnightDateGMT, $midnightTimeGMT, $midnightDate, $dayEndTime, $sensorId);