When would a Nonunique Primary Index (NUPI) be required instead of a Unique Primary Index (UPI)?

A Nonunique Primary Index (NUPI) is utilized when the Primary Index column or columns contain duplicate values. In Teradata, the purpose of a primary index is to distribute data across AMPs (Access Module Processors) evenly for efficient access and retrieval. If a column designated as the primary index has duplicate values, it cannot be a Unique Primary Index (UPI) because UPI requires that each value in the primary index be distinct for every row.

By defining a NUPI on these duplicate values, Teradata allows for multiple rows to be associated with the same index value. This arrangement ensures that although data may duplicate, it can still be efficiently accessed and managed within the Teradata system. In contrast, a UPI would require distinct values for each row, which is not feasible in this scenario.

The other options do not compel the use of a Nonunique Primary Index specifically. Optimized data compression is not determined by the uniqueness of the primary index, as it relates more to data characteristics and storage efficiency. Similarly, the absence of duplicate values directly leads to the use of a Unique Primary Index, not a Nonunique one, and enhancing query performance can be achieved through various methods, not just through the choice of primary index type