You can use any value expression including subqueries,
    conditional, character, date/time, and numeric expressions as
    default values. See Value Expressions for more information about
    value expressions.

    The value expressions described in Value Expressions include
    DBKEY and aggregate functions. However, the DEFAULT clause is
    not a valid location for referencing a DBKEY or an aggregate
    function. If you attempt to reference either, you receive a
    compile-time error.