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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Answer / farooq
explain provides execution procedure(stratergy).It gives
the estimated time,confidence and memory needed to execute
the query.It is used to analayze all joins and complex
queries.
"EXPLAIN parses the sql atatement but does not execute it".
| Is This Answer Correct ? | 24 Yes | 1 No |
Answer / adi
explain gives the execution strategy means what are the
different steps that the query will go through.
HIGH CONFIDENCE:Statistics are collected.
LOW CONFIDENCE:Statistics are not collected. But the where
condition is having the condition on indexed column. Then
estimations can be based on sampling.
NO CONFIDENCE:Statistics are not collected and the
condition is on non indexec column.
| Is This Answer Correct ? | 18 Yes | 3 No |
Answer / farooq
HIGH CONFIDENCE:Statistics are collected up to date.
LOW CONFIDENCE:Statistics are not up todate.
NO CONFIDENCE:Statistics are not collected.
| Is This Answer Correct ? | 16 Yes | 2 No |
Answer / yuvaevergreen
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 column
or 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.
| Is This Answer Correct ? | 8 Yes | 1 No |
Answer / yuvaevergreen
1.Explain helps us to know about the stats needed.
| Is This Answer Correct ? | 3 Yes | 6 No |
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