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Teradata - What EXPLAIN does in Teradata, what is High confidence, Low confidence and No confidence. And How we improve the query performance ?




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asked mar September 20, 2014 06:38 AM  

What EXPLAIN does in Teradata, what is High confidence, Low confidence and No confidence. And How we improve the query performance ?


           

1 Answers



 
answered By vishnoiprem   0  
The explain generally displays the plan which would be prepared by Optimizer.We can say that(though not accurate)
plan would be the steps followed by Teradata to solve a query.Confidence levels indicate how well the optimizer is aware about the demographic data for a particular step.

High confidence: Means the optimizer know about the no of rows that would be returned as a result of that step.
Examples would be when PI statistics exist when the columnor range stats exist or no join involved.

Low confidence: Some stats available. Join and stats available on both sides of the join.

No confidence: No stats available. Join involved.
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