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Message Posted: Tue, 19 Feb 2008 @ 16:38:04 GMT

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Subj:   Re: High confidence in Explain
From:   Michael Larkins

Guten Tag Martin:

  From my experience "high confidence" means that statistics have been collected.  

What is does not mean:

1. that they are current because rows have been inserted or deleted since the last collect operation

2. that all columns of the WHERE clause have collected statistics on them

3. that single column versus multi-column statistics are available

From my perspective, if you are within 25% that isn't all that bad. The main thing you want to verify is that the results stated in the EXPLAIN (before a single row of user data has been accessed) is that the values are "reasonable." You certainly don't want to see 17,000,000,000 rows with an estimate of 256,000 hrs. From the sounds of your EXPLAIN, it is very reasonable.

Mit freundlichen Grüßen, sie auch

Michael Larkins
Certified Teradata Master
Certified Teradata SQL Instructor

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