A unique index, like a primary key, has a unique value for each row in a table.
Teradata defines two different unique indexes:
- Unique primary index (UPI)
UPIs provide optimal data distribution and are typically assigned to the primary key for a table. When a NUPI makes better sense for a table, then the primary key is frequently assigned to be a USI.
- Unique secondary index (USI)
USIs guarantee that each complete index value is unique, while ensuring that data access based on it is always a two-AMP operation.