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Teradata - Why Primary Index is required in the Teradata ?

asked vishnoiprem August 17, 2014 04:35 AM  

Why Primary Index is required in the Teradata ?


1 Answers

answered By vishnoiprem   0  
Every table must have at least one column as the Primary Index. The Primary Index is defined when the table is created. There are only two types of Primary Indexes, which are a Unique Primary Index (UPI) or a Non-Unique Primary Index (NUPI). Because Teradata distributes the data based on the Primary Index columns value it is quite obvious that you must have a primary index and that there can be only one primary index per table. The Primary index is the Physical Mechanism used to retrieve and distribute data. The primary index is limited to the number of columns in the primary index. In other words,the primary index is made up of from 1 to 16 columns. You can pick only one primary index and once it is picked you will need to access all columns in the WHERE clause for the primary index to be utilized on the retrieve. Most databases use the Primary Key as the physical mechanism. Teradata uses the Primary Index. There are two reasons you might pick a different Primary Index then your Primary Key. They are (1) for Performance reasons and (2) known access paths.
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