Index Cocepts in Teradata - response (12) by M.Saeed Khurram

Hi Ratnam,
Basically these three are join processing strategies used by Teradata, and decided by the oprimizer based on number of factors. I think they are not availbel for the developer to choose between. You can see these words in the explain plan and on the basis of explain you can tune your queries to use one of these. 
Any of these types can be better based on the workload and query types. Merge Join is mostly used when both the tables participating in join have PI on joining columns. Nested joins are mostly useful in OLTP applications where one table is higly selective and the other table is processed based on a selected row from one table.