查询一个表占用了多大的表空间

SELECT   owner,
         DECODE (partition_name,
                 NULL, segment_name,
                 segment_name || ':' || partition_name
                ) NAME,
         segment_type, tablespace_name, BYTES/1024/1024 , initial_extent, next_extent,
         pct_increase, extents, max_extents
    FROM dba_segments
   WHERE 1 = 1 AND extents > 1
ORDER BY 9 DESC, 3

也可以这样,查一个表占用的总空间:
select trunc(sum(bytes)/1024/1024,3) from dba_segments
where segment_name=&table_name and
owner=&owner_name