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    Teradata Architecture for IT and Developers   by Tom Coffing and John Nolan Coffing Data Warehousing. (c) 2013. Copying Prohibited. Reprinted for Chaitanya Paruchuri, Accenture   chaitanya.paruchuri@accenture.com   Reprinted with permission as a subscription benefit of Skillport , http://skillport.books24x7.com/   All rights reserved. Reproduction and/or distribution in whole or in part in electronic,paper or other forms without written permission is prohibited.    Chapter 2: The Primary Index Overview He who walks in another's tracks leaves no footprints. - Joan L. Brannon The Primary Index is defined when the table is CREATED The Primary Index is defined when the table is CREATED. Above, we have a UPI which stands for a Unique Primary Index (UPI). A Unique Primary Index (UPI) Teradata Architecture for IT and DevelopersReprinted for OET7P/994216, Accenture Coffing Data Warehousing, Coffing Publishing (c) 2013, Copying Prohibited Page 2 / 9    A Unique Primary Index (UPI) spreads the rows of a table evenly across the AMPs. Primary Index in the WHERE Clause - Single-AMP Retrieve Use the Primary Index column in your SQL WHERE clause and only 1-AMP retrieves. Using EXPLAIN Emp_No Dept_No First_Name Last_Name Salary   1005 400 Rob Rivers 50000   Teradata Architecture for IT and DevelopersReprinted for OET7P/994216, Accenture Coffing Data Warehousing, Coffing Publishing (c) 2013, Copying Prohibited Page 3 / 9   If you want to see the Parsing Engine's plan, all you have to do is type EXPLAIN in front of your SQL. You can also hit the Function Key F6, or click on the magnifying glass on Nexus. Above, you can see that we are doing a single-AMP RETRIEVE step by way of a Unique Primary Index (UPI). A Non-Unique Primary Index (NUPI)  A Non-Unique Primary Index (NUPI) will have duplicates grouped together on the same AMP, so data will always be skewed (uneven). The above skew is reasonable. Primary Index in the WHERE Clause - Single-AMP Retrieve Teradata Architecture for IT and DevelopersReprinted for OET7P/994216, Accenture Coffing Data Warehousing, Coffing Publishing (c) 2013, Copying Prohibited Page 4 / 9
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