Consultar Tamanho de tabelas em Oracle

select --'truncate table ' || segment_name || ';',
       segment_name table_name, sum(bytes) / (1024 * 1024) table_size_meg
  from user_extents
 where segment_type = 'TABLE'
--   and segment_name = 'MyTable1'
 group BY segment_name
 HAVING sum(bytes) / (1024 * 1024) > 5 -- Mega