Oracle NoSQL Database does not currently support the general join operators found in more traditional relational database systems. However, it does support a special kind of join among tables that belong to the same table hierarchy. These joins can be executed efficiently, because only co-located rows may match with each other. As a result, transferring very large amounts of data among servers is avoided.

A JOIN clause is used to combine rows from two or more tables, based on a related column between them. Joins are predominantly used in an Oracle NoSQL Database when a user is trying to extract data from tables that have a hierarchical relationship between them. For more details on hierarchical tables, see Table Hierarchies.

There are three ways by which you can join tables in the same hierarchy in an Oracle NoSQL Database.

• NESTED TABLES
• Left Outer Join
• Inner Join