Assigning a DEFAULT USER to a column identifies the person making an entry in a database. This information may be required; for example, when salespeople are working on commission.
Building a user ID default into the primary key of a table is a useful technique for occasionally connected users, and helps prevent conflicts during information updates. These users can make a copy of the tables that are relevant to their work on a portable computer, make changes while not connected to a multiuser database, and then apply the transaction log to the server when they return.
The special values USER and CURRENT USER return a string that contains the user ID of the current connection and can be used as a default value in columns with character data types. On UPDATE, columns with a default value of USER or CURRENT USER are not changed.
The special value LAST USER returns the name of the user who last modified the row and can be used as a default value in columns with character data types. On INSERT and LOAD, this constant has the same effect as CURRENT USER. On UPDATE, if a column with a default value of LAST USER is not explicitly modified, it is changed to the name of the current user.
When combined with the DEFAULT TIMESTAMP, a default value of LAST USER can be used to record (in separate columns) both the user and the date and time a row was last changed.