Alter database datafile resize. January 28, 2023July 20, 2018 by Sajid QuamerIf we want to resize the existing data file. We must use alter database datafile resize command.Steps to resize using alter database datafile resize. alter database datafile resize Before doing resize the data file in oracle database, we will have to check the existing data file size. SQL>select file_name,bytes/1024/1024 SIZE_IN_MB from dba_data_files where tablespace_name=’XXCUSTOM’; Resize the oracle database data file using below command. SQL>alter database datafile ‘/path/filename.dbf’ resize 6g; To enable auto-extend on datafile, click here. For additional information on Administering Database Size. Please check.👉alter tablespace add datafile.