select tablespace_name ,sum(bytes) / 1024 / 1024 as MB from dba_data_files group by tablespace_name;

2. View all tablespace corresponding datafiles:

select tablespace_name,file_name from dba_data_files;

3, modify the datafile size:

alter database datafile 'H:\ORACLE\PRODUCT\ 10.1.0\ORADATA\ORACLE\USERS01.DBF' RESIZE 10240M;