UNDO Space usage question

[Lipman Li]

A user is executing a transaction in an Oracle database. Which of the following choices correctly identifies all the statements that will generate undo information within the transaction?
A . insert statements only
B . update and insert statements only
C . delete statements only
D*. delete and update statements only
E . delete, insert, and update statements only
could not understand why choice D is correct, I remember that insert also put some information (such as ROWID) into undo segament, otherwise how oracle could rollback?
could anyone kindly explain?
thanks

[Beksy Kurian]

I would say 'least undo' for insert rather than saying no undo at all.
when we rollback:
delete requires reinserting the row(reconstruct the actual row)
insert requires just to delete the row (takes less bytes to store a rowid).
Hummm! If the question was not 'least undo', I would have given the answer 'E' and gotten a score 0.

Regards
Beksy
[ October 03, 2002: Message edited by: Beksy Kurian ]