I need a select from table which does not have column that tells when row was inserted, only timestamp column (values like: 0x0000000000530278). Some data was i
To identify new rows by timestamp you need to keep track of the timestamps that were there beforehand. In a pinch you could:
With a minor risk of false positives if anything else has been going on in the DB this will get you a reasonably good difference.
For a more robust check you could calculate MD5 or SHA-1 hashes with Hashbytes on the row contents to give you a difference with a very low probability of collision (see this wikipedia article on Birthday attacks for a discussion of this problem).