You might think that the content of a normal data file should be unrecognized binary text and we cannot really see it except using special tools. Actually, you can see more than you thought.
In this post, I will show you what we can see in a normal data file without using SQL as the interface language.
Actually, I used a very common text editor vi in Linux to inspect a data file named example01.dbf which contains sample schemas and data.
[oracle@test ~]$ cd $ORACLE_BASE/oradata/COMPDB/
[oracle@test COMPDB]$ vi example01.dbf -c "se nu"
Plain Text in Data Files
I highlighted some clear text that I can recognize on the screenshot. In fact, what we see above from line #10 to #13 is a portion of table HR.LOCATIONS. That is to say, the content of a normal data file can be seen by common means. Anyone has the right to access data files is capable of getting a useful copy of them.
Don't be surprised, it has been a long time to be some degree of plaintext in normal data files. If you concern about it, you should go for Oracle Transparent Data Encryption (TDE).
Normally, we use data files starting with creating them, there're some restrictions that we should notice on adding data files to a tablespace.