ASA SQL User's Guide
Ensuring Data Integrity
Using column defaults
For columns with the DATE, TIME, or TIMESTAMP data type, you can use the current date, current time, or current timestamp as a default. The default you choose must be compatible with the column's data type.
A current date default might be useful to record:
dates of phone calls in a contact database
dates of orders in a sales entry database
the date a patron borrows a book in a library database
The current timestamp is similar to the current date default, but offers greater accuracy. For example, a user of a contact management application may have several contacts with a single customer in one day: the current timestamp default would be useful to distinguish these contacts.
Since it records a date and the time down to a precision of millionths of a second, you may also find the current timestamp useful when the sequence of events is important in a database.
For more information about timestamps, times, and dates, see SQL Data Types.