0 - 2 of 2 tags for primary indexes

I need some general guidance on choosing a new PI to make table A more easily accessible in joins.
 
If my join looks like this:
 
LEFT JOIN A
  ON A.INVC_ID = B.INVC_ID
 AND A.DTA_SRC_ID = B.DTA_SRC_ID

Some of you may be familiar with relational databases other than Teradata and how those other RDBMs utilize indexes.

In Teradata, an “Index” is a physical mechanism that is used to distribute, store, and access data rows. Indexes provide a physical access path to the data and their use can avoid unnecessary full-table scans to locate rows.