Table Hierarchies

The Oracle NoSQL Database enables tables to exist in a parent-child relationship. This is known as table hierarchies.

The create table statement allows for a table to be created as a child of another table, which then becomes the parent of the new table. This is done by using a composite name (name_path) for the child table. A composite name consists of a number N (N > 1) of identifiers separated by dots. The last identifier is the local name of the child table and the first N-1 identifiers point to the name of the parent.

Characteristics of parent-child tables:

• A child table inherits the primary key columns of its parent table.

• All tables in the hierarchy have the same shard key columns, which are specified in the create table statement of the root table.

• A parent table cannot be dropped before its children are dropped.

• A referential integrity constraint is not enforced in a parent-child table.

You should consider using child tables when some form of data normalization is required. Child tables can also be a good choice when modeling 1 to N relationships and also provide ACID transaction semantics when writing multiple records in a parent-child hierarchy.