select decode( grouping(nm), 1, 'total', nm ) nm, round(sum(val/1024/1024)) mb
from
(
	select 'sga' nm, sum(value) val from v$sga
	union all
	select 'pga', sum(a.value) from v$sesstat a, v$statname b where b.name = 'session pga memory' and a.statistic# = b.statistic#
)
group by rollup(nm);


NM            MB
----- ----------
pga          606
sga         5008
total       5614