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Message Posted: Wed, 10 Sep 2002 @ 21:22:35 GMT


     
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Subj:   Re: OLAP function Spool Usage
 
From:   Klavs Raats

Jeremy,

I found some clues from description of Teradata OLAP functions:

***
Many common operations necessary in analytical processing and data mining environments cannot be expressed with standard ANSI SQL queries, either because they require an ordered set of results rows, or a calculation depends on values in a previous row.

. First, that rows be ordered by ordering column(s)

. Then, the value for the running sum must be computed,

- Adding the current row value to the value of the sum from the previous row, and

- subtracting the value from the last row of the previous group. ***

Because of necessity to order rows by values of A.COLUMN_1, A.COLUMN_2 (in EXPLAIN: which is assumed to be redistributed by value to all AMPs) distribution of spool is not as good as with hash.

Klavs



     
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