DEFAULT Function in SELECT Statements
The rules and restrictions are:
The DEFAULT function accepts a single expression that identifies a relation column
by name. The function evaluates to a value equal to the current default value for
the column. For cases where the default value of the column is specified as a current
built‑in system function, the DEFAULT function evaluates to the current value of system
variables at the time the request is executed.
The resulting data type of the DEFAULT function is the data type of the constant or
built‑in function specified as the default unless the default is NULL. If the default
is NULL, the resulting date type of the DEFAULT function is the same as the data type
of the column or expression for which the default is being requested.
The DEFAULT function can be specified as DEFAULT or DEFAULT(column_name). When column name is not specified, 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 in the select list of a SELECT
statement. The DEFAULT function evaluates to the default value of the specified column.
The DEFAULT function must include a column name in the expression list.
You can determine the default value for a column by selecting it without specifying
a FROM clause for the statement.
When you specify a SELECT statement that does not also specify a FROM clause, the
system always returns only a single row with the default value of the column, regardless
of how many rows are in the table. This is similar to the behavior of the TYPE function.
When the column passed as an input argument to the DEFAULT function does not have
an explicit default value associated with it, the DEFAULT function evaluates to null.