In the second example, the length definition of department has been changed to 32. Adding Constraints to Table Definition Users can specify constraints on columns in tables. Row insertion and updates on tables will fail if these constraints are violated. Constraints can be specified either during or after table creation. Constraints can be disabled and re-enabled.
Users can assign a name to a constraint.
This practice of naming your constraints is highly recommended and valuable . If you do not assign a name, Oracle will assign a name for you. When a constraint is violated, Oracle reports the name of the constraint that has been violated. If you name your constraints, then you can easily identified what table and type of constraint. It is useful to follow a naming convention when assigning names to your constraints.