Defining the primary index (PI) for a table is the most critical aspect of table design.
The system uses the PI to assign each data row to an Access Module Processor (AMP). A well chosen PI balances the distribution across AMPs and helps optimize the performance of queries that access the table. PIs also enable efficient joins and aggregations.
A Teradata Database query does not use a PI for access unless all columns in the index are in an equality predicate or an IN LIST.
After you identify the PI requirements for a table, you specify the PI as part of the CREATE TABLE statement.