What is the primary purpose of a Join Index (JI) in Teradata?

The primary purpose of a Join Index (JI) in Teradata is to improve performance for complex queries. A Join Index serves as a pre-aggregated, pre-joined representation of data that simplifies and speeds up the execution of join operations. When a query involves joining multiple tables, Teradata can utilize the Join Index to avoid costly operations of combining tables during query execution, resulting in faster response times.

Join Indexes can be particularly useful in scenarios where queries frequently access the same combination of tables, allowing for efficient access to the already joined data. This optimized data access not only reduces the CPU time required for complex queries but also minimizes input/output operations, enhancing overall performance.

The other options do not accurately capture the primary purpose of a Join Index. While ensuring unique identification of rows is important in database management, it is not the main function of a Join Index. Similarly, while access paths are essential in query processing, they pertain more broadly to how data is retrieved rather than the specific optimization provided by Join Indexes. Lastly, sorting of rows is more related to partitioning schemes and data organization rather than the direct purpose of a Join Index.