Using NESTED TABLES to join parent-child tables
A JOIN is used to combine rows from two or more tables, based on a related column
                        between them. In a hierarchical table, the child table inherits the primary
                        key columns of its parent table. This is done implicitly, without including
                        the parent columns in the CREATE TABLE statement of the
                        child. All tables in the hierarchy have the same shard key columns.
               
You can use NESTED TABLES clause to join tables in Oracle NoSQL Database.