Retrieving Username Using Oracle Triggers

I am new to using triggers. What function can I use to determine who tripped my trigger?

For example:开发者_如何转开发

Someone updates a row, and I want to know who updated the row.

I am using Oracle 10g.

SELECT sys_context('USERENV', 'SESSION_USER') FROM dual;

or

SELECT sys_context('USERENV', 'SESSION_USERID') FROM dual;