Index in Teradata

What is index. How many types of indexes in Teradata.
=> Index is physical mechanism which is used to access and distribute the data rows.
      Indexes help to fast retrieval of data set and useful to data distribution across AMP.

=>There are four main types of indexes in Teradata.
    * Primary Index
    * Secondary Index
    * Join Index
    * Hash Index

=> These indexes divided into following sub category.
    * Unique Primary Index (UPI)
    * Non-Unique Primary Index (NUPI)
    * Partitioned Primary Index(PPI)
    * Non-Partitioned Primary Index(NPPI)
    * Unique Secondary Index (USI)
    * Non-Unique Secondary Index (NUPI)

=> Join Index has six subtypes viz:
    * Single table join index(STJI)
    * Single table aggregate join index(STAJI)
    * Single table sparse join index
    * Multitable simple join index
    * Multitable aggregate join index
    * Multitable sparse join index