All AMP Operations vs Full Table Scan

All AMP Operation (NUSI) :
1. The SQL is submitted, specifying a NUSI.The hashing algorithm calculates a row hash value for
the NUSI .
2. All AMPs are activated to find the hash value of the NUSI in their index subtables. The AMPs
whose subtables contain that value become the participating AMPs in this request The other
AMPs discard the message.
3. Each participating AMP locates the row IDs (row hash value plus uniqueness value) of the base
rows corresponding to the hash value.
4. The participating AMPs access the base table rows, which are located on the same AMP as the
NUSI subtable.
5. The qualifying rows are sent over the BYNET to the PE, and the PE sends the answer set on to
the client application .


Full-Table Scan : (Accessing data with out indexes) :
If the request does not use a defined index, the Teradata Database does a full-table scan. A full-table scan is another way to access data without using Primary or Secondary Indexes. In evaluating an SQL request, the Optimizer examines all possible access methods and chooses the one it believes to be the most efficient.

A request could turn into a full-table scan when:
The SQL request searches on a NUSI column with many duplicates.
An SQL request uses a non-equality WHERE clause on an index column.
An SQL request uses a range WHERE clause on an index column.

For all requests, you must specify a value for each column in the index