Types of Indexes
A unique index column set, like a primary key column set constraint, enforces a unique value for that column set for each row in a table.
Teradata Database defines two different types of unique index:
UPIs provide optimal data distribution and, when used, are typically assigned to the primary key for a table.
UPIs are described in detail in “Unique Primary Indexes” on page 264.
USIs guarantee that each complete index value is unique, while ensuring that data access based on it is always at most a two-AMP operation. A USI is typically assigned to the primary key for a table when the table does not have a UPI for the primary key and enforcement by the system of a primary key or unique constraint is a requirement.
USIs are described in detail in “Unique Secondary Indexes” on page 457.