A default value control phrase determines the action to take when you do not supply
a value for a field.
The following rules and guidelines apply to default value control phrases:
Default value control phrases are only valid with the following data definitions.
Fields defined in CREATE TABLE and ALTER TABLE statements
Parameters defined in CREATE MACRO and REPLACE MACRO statements
Default value controls are not effective for views and expressions.
The default value for a field is null unless you specify NOT NULL, in which case there
is no default value if you do not specify the DEFAULT phrase.
The presence of nulls can affect query performance negatively; therefore, consider
using the NOT NULL default value phrase unless you intend to have nulls in the column.
The default control value phrases are documented individually in the remaining topics
in this chapter.