Restrictions on Table Hierarchies

Inheritance occurs in one direction only, namely from supertable to subtable. Properties of subtables are not inherited by supertables. The section System Catalog Information lists the inherited database objects for which the system catalog maintains no information regarding subtables.

No two tables in a table hierarchy can have the same data type. For example, the final line of the next code example is invalid, because the tables tab2 and tab3 cannot have the same row type (rowtype2): 
         create row type rowtype1 (...);
         create row type rowtype2 (...) under rowtype1;
         create table tab1 of type rowtype1;
         create table tab2 of type rowtype2 under tab1;
         create table tab3 of type rowtype2 under tab1; -- This is not valid.