Defaults allow you to specify a value to be entered into a column, if one is not otherwise specified. Defaults can be anything that evaluates to a constant, such as a constant, a built-in function, or a mathematical expression. Defaults are of two types: declarative and bound. The two are functionally the same; the difference is in how they are implemented.
A declarative default is just another flavor of constraint, and as such is implemented using the CREATE TABLE and ALTER TABLE commands. Following is an example of adding a DEFAULT constraint to the employee table that enters a value of UNLISTED if no phone number is specified:
ALTER TABLE employee ADD CONSTRAINT df_emp_ph DEFAULT 'UNLISTED' FOR Phone
To remove ...