Which feature is associated with Primary Index (PI) in Teradata?

The feature associated with the Primary Index (PI) in Teradata is that it may consist of multiple columns. A Primary Index is a crucial component in Teradata's architecture as it determines how the data is distributed across the different nodes in the system. When defining the Primary Index, users have the option to include more than one column, which is known as a composite primary index.

This capability allows for more efficient data access and can improve query performance, especially when queries filter on multiple columns that are part of the index. By using multiple columns in the Primary Index, Teradata can better align data distribution with how applications access the data, leading to optimized performance.

The other options do not accurately represent the functionality or characteristics of Primary Indexes in Teradata. While sorting rows by partition is more related to partitioned primary indexes, and the restriction on null values typically pertains to how primary indexes are defined, it is the support for multiple columns that distinctly highlights the flexibility and power of Primary Indexes in the Teradata system.