Tuesday, October 23, 2012

What is High confidence, Low confidence and No confidence in EXPLAIN plan?

Explain gives the execution strategy based on dictionary information (stats) it has about object in questions.

  • HIGH CONFIDENCE: Statistics are collected.
  • LOW CONFIDENCE: Statistics are not collected.But the where condition is having the condition on indexedcolumn.Then estimations can be based on sampling.
  • NO CONFIDENCE: Statistics are not collected and the condition is on non indexed column

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