The DEFAULT function can be specified as DEFAULT or DEFAULT (column_name). When you do not specify a column name, the system derives the column based on context. If the column context cannot be derived, the system returns an error.
You can specify a DEFAULT function with a column name argument within a predicate. The system evaluates the DEFAULT function to the default value of the column specified as its argument. Once the system has evaluated the DEFAULT function, it treats it like a constant in the predicate.
You can specify a DEFAULT function without a column name argument within a predicate only if there is one column specification and one DEFAULT function as the terms on each side of the comparison operator within the expression.