How Teradata determines primary index
Every table must have at least one column as the Primary Index. The Primary Index is defined when the table is created.There are two reasons you might pick a different Primary Index then your Primary Key. They are (1) for Performance reasons and (2) known access paths. Primary Index Rules Rule 1: One Primary Index per table. Rule 2: A Primary Index value can be unique or non-unique. Rule 3: The Primary Index value can be NULL. Rule 4: The Primary Index value can be modified. Rule 5: The Primary Index of a populated table cannot be modified. Rule 6: A Primary Index has a limit of 64 columns. Two Types of Primary Indexes (UPI or NUPI) Unique Primary Index(UPI) - A Unique Primary Index (UPI) is unique and cannot have any duplicates. If you try and insert a row with a Primary Index value that is already in the table, the row will be rejected. An UPI enforces UNIQUENESS for a column Non-Unique Primary Index (NUPI) - A Non-Unique Primary Index (NUPI) means that the v...