Oracle resets the data file size

SQL> select file_id, tablespace_name, file_name, bytes/(1024*1024) as MB from dba_data_files where tablespace_name like 'test _ T % ';

 

FILE_ID TABLESPACE_NAME FILE_NAME MB

---------------------------------------------------------------------------

7 TEST_TAB/home/Oracle/oracle/oradata/mdsp/test_ta 20

B. dbf

 

 

SQL> alter database datafile '/home/oracle/oradata/mdsp/test_tab.dbf' resize 21 m;

 

Database altered.

 

SQL> select file_id, tablespace_name, file_name, bytes/(1024*1024) as MB from dba_data_files where tablespace_name like 'test _ T % ';

 

FILE_ID TABLESPACE_NAME FILE_NAME MB

---------------------------------------------------------------------------

7 TEST_TAB/home/oracle/oradata/mdsp/test_ta 21

B. dbf

SQL> alter tablespace test_tab add datafile '/home/oracle/oradata/mdsp/test_tab1.dbf' size 20 m;

 

Tablespace altered.

 

SQL> select file_id, tablespace_name, file_name, bytes/(1024*1024) as MB from dba_data_files where tablespace_name like 'test _ T % ';

 

FILE_ID TABLESPACE_NAME FILE_NAME MB

---------------------------------------------------------------------------

7 TEST_TAB/home/oracle/oradata/mdsp/test_ta 21

B. dbf

 

8 TEST_TAB/home/oracle/oradata/mdsp/test_ta 20