Aman Sinha created DRILL-7187:
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Summary: Improve selectivity estimates for range predicates when
using histogram
Key: DRILL-7187
URL: https://issues.apache.org/jira/browse/DRILL-7187
Project: Apache Drill
Issue Type: Bug
Reporter: Aman Sinha
Assignee: Aman Sinha
2 types of selectivity estimation improvements need to be done:
1. For range predicates on the same column, we need to collect all such
predicates in 1 group and do a histogram lookup for them together.
For instance:
{noformat}
WHERE a > 10 AND b < 20 AND c = 100 AND a <= 50 AND b < 50
{noformat}
Currently, the Drill behavior is to treat each of the conjuncts independently
and multiply the individual selectivities. However, that will not give the
accurate estimates. Here, we want to group the predicates on 'a' together and
do a single lookup. Similarly for 'b'.
2. NULLs are not maintained by the histogram but when doing the selectivity
calculations, the histogram should use the totalRowCount as the denominator
rather than the non-null count.
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