Home Page for the TeradataForum

Archives of the TeradataForum

Message Posted: Mon, 02 Nov 2015 @ 20:42:30 GMT

  <Prev Next>   <<First <Prev Next> Last>>  

Subj:   Re: Multiple single-column SI vs Single Multi-column SI
From:   Anomy Anom

<-- Anonymously Posted: Monday, November 02, 2015 17:32 -->

The USI row contains the actual column values as well as the RowHash of those values and the RowID of the base row. No, you won't know which AMP to check, but it may be cheaper to scan the USI subtable on all AMPs than to scan the table.

For a NUSI, the index "rows" are not hashed, they are locally ordered and always scanned rather than being accessed directly. ORDER BY HASH provides a pseudo-random order while ORDER BY VALUES may allow you to skip forward and/or terminate the scan early.

  <Prev Next>   <<First <Prev Next> Last>>  
  Top Home Privacy Feedback  
Copyright for the TeradataForum (TDATA-L), Manta BlueSky    
Copyright 2016 - All Rights Reserved    
Last Modified: 24 Jul 2020