Originally posted by Fiza15
will it give me error mssge that i cant resize because there are DB Blocks having data
Yes, you're very confused. If you are getting this error message, you are trying to shrink your data file.

For example:
Code:
SQL> select file_name, bytes/1024/1024 mb
  2  from dba_data_files
  3  where tablespace_name = 'USERS';

FILE_NAME                                                      MB
------------------------------------------------------ ----------
E:\ORADATA\NT817\USERS01.DBF                                    4

SQL> alter database datafile 'E:\ORADATA\NT817\USERS01.DBF' resize 1M;
alter database datafile 'E:\ORADATA\NT817\USERS01.DBF' resize 1M
*
ERROR at line 1:
ORA-03297: file contains used data beyond requested RESIZE value


SQL> alter database datafile 'E:\ORADATA\NT817\USERS01.DBF' resize 5M;

Database altered.

SQL> select file_name, bytes/1024/1024 mb
  2  from dba_data_files
  3  where tablespace_name = 'USERS';

FILE_NAME                                                      MB
------------------------------------------------------ ----------
E:\ORADATA\NT817\USERS01.DBF                                    5