Because sometimes the user give up to include a record (revert) and that number of autoinc field is not used. It is not a problem, just a preference of user.

>I don't think so because it would cause problem if 2 transactions occurs at the same time and that you need the autoinc field to do relation in your transaction.
>
>The real question is: why do you need the autoinc field to increment only when tapleupdate is issued?
>
>>I would like to increment autoinc field just when tableupdate is issued. Is it possible?