Type Hierarchies

When you create a subtype, you create a type hierarchy. In a type hierarchy, each subtype that you create inherits its properties from a single supertype. If you create a named ROW type customer_t under person_t, customer_t inherits all the fields of person_t. If you create another named ROW type, salesrep_t under customer_t, salesrep_t inherits all the fields of customer_t.

Thus, salesrep_t inherits all the fields that customer_t inherited from person_t as well as all the fields defined specifically for customer_t. For a discussion of type inheritance, refer to the HCL OneDB™ Guide to SQL: Tutorial.