The DEFAULT function returns the default value of a column. It has two forms: one that specifies a column name and one that omits the column name.
Predicates using comparison operators support both forms of the DEFAULT function, but when the DEFAULT function omits the column name, the following conditions must be true:
- The comparison can only involve a single column reference.
- The DEFAULT function cannot be part of an expression.
For example, the following statement uses DEFAULT to compare the values of the Dept_No column with the default value of the Dept_No column. Because the comparison operation involves a single column reference, Teradata Database can derive the column context of the DEFAULT function even though the column name is omitted.
SELECT * FROM Employee WHERE Dept_No < DEFAULT;
Note that if the DEFAULT function evaluates to null, the predicate is unknown and the WHERE condition is false.