mem_usage2.sql

col TOTAL           heading 'Total|Memory Usage'        format 999,999,999

compute sum of TOTAL on report
break on report

select NVL(vs.username,'ORACLE') "USER",
       SUM(se.value) TOTAL
from v$sesstat se,
     v$statname n,
     v$session vs
where n.statistic# = se.statistic#
and   n.name in ('session pga memory max'
                 )
and vs.sid         = se.sid                 
group by vs.username
order by 2 desc
/