select owner, table_name, sum(size_m)
from (select s.owner,
s.segment_name as table_name,
s.bytes / 1024 / 1024 as size_m
from dba_segments s, dba_tables t
where s.owner = t.owner
and s.segment_name = t.table_name
union
select s.owner,
l.table_name as table_name,
s.bytes / 1024 / 1024 as size_m
from dba_segments s, dba_lobs l
where s.owner = l.owner
and s.segment_name = l.segment_name
union
select s.owner,
i.table_name as table_name,
s.bytes / 1024 / 1024 as size_m
from dba_segments s, dba_indexes i
where s.owner = i.owner
and s.segment_name = i.index_name
union
select s.owner,
p.table_name as table_name,
s.bytes / 1024 / 1024 as size_m
from dba_segments s, dba_tab_partitions p
where s.owner = p.table_owner
and s.segment_name = p.partition_name)
group by owner, table_name
order by sum(size_m) desc