One must not get confused between Primary Key and Primary Index in Teradata. Primary KEY is more of a logical thing however Primary INDEX is more of physical thing. In Teradata, Primary INDEX is used for finding best access path for data retrieval and data insertion and Primary KEY is used for finding each rows uniquely just like in other RDBMS. So below are few differences between PRIMARY KEY and PRIMARY INDEX:
PRIMARY KEY cannot be NULL
PRIMARY KEY is not mandatory in Teradata
PRIMARY KEY does not help in data distribution.
PRIMARY KEY should be unique.
PRIMARY KEY is logical implementation.
PRIMARY INDEX can be NULL
PRIMARY INDEX is mandatory In Teradata
PRIMARY INDEX helps in data distribution.
PRIMARY INDEX can be UNIQUE (Unique Primary Index) or NON UNIQUE (Primary Index).