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Estimating the cost of a plan

Table statistics

Estimating selectivity


select *
from Employee
where age between 50 and 55

Use the index or scan the table?

between 50 and 55 is covered by two buckets:
- 48-52: 3/5 of 101 = 60.6
- 53-57: 3/5 of 97 = 58.2
- Total: 118.8
Selectivity is 118.8 / 710 = 16.7%.

Over 10%: Don't use the index!

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