Is it possible to get username information while writing trigger?

Hey:

What I want is to add a log entry at the last column of each row, which will record the history update, insert automatically when relative statement is processed.

I have read the documentation on triggers, which helps a lot. However, I may have few more extra requirement to complete my wishes:

1, I would like to get the username of who executed the statement;

2, I would like to get the column name that is being updated;

If it is possible and how should I do it??

Thanks a lot!