1.通过查询dba_segments
Select owner,segment_name,sum(bytes)/1024/1024 as MB from dba_segments group by owner,segment_name;
查询：是分配给一个表的物理空间数量，而不管空间是否被使用。
2.num_rows * avg_row_len
select table_name, round(num_rows * avg_row_len /1024/1024, 8) as total_len, num_rows from all_tables where table_name = '表名' order by table_name;
查到的是实际占用的空间大小，已经使用的