Does every table has primary index in Teradata?

PI is so important to Teradata functionality that every table in the database is required to have one
The Main uses of PI are

1. The Primary Index WILL DETERMINE which rows go to which AMPs; and

2. The Primary Index is ALWAYS the FASTEST RETRIEVAL method.

if the user doesn't define a PRIMARY INDEX when creating a table, the system will automatically choose one by default. Once it is defined, the PI column cannot be dropped or changed. The table would need to be re-created in order to change the PI.