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https://issues.apache.org/jira/browse/DERBY-6938?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16048798#comment-16048798
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Harshvardhan Gupta commented on DERBY-6938:
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The specific approach I am thinking is to keep the minimum and maximum value of
columns and number of NULL values in statistics, this could be utilised in
operators such as (< , > , <=, >=, IS NOT NULL, NULL) etc.
For example, lets say we have a int column and the minimum and maximum value is
20 and 100 respectively. Then for a query predicate on that column with the
condition that >=80 should ideally return 25% of all columns. This approach
obviously assumes an uniform distribution but should be good to get started
with. We should be able to make it more efficient by taking into account
distribution later on.
> Obtain cardinality estimates and true estimates for base tables as well as
> for intermediate results for queries involving multiple joins.
> -------------------------------------------------------------------------------------------------------------------------------------------
>
> Key: DERBY-6938
> URL: https://issues.apache.org/jira/browse/DERBY-6938
> Project: Derby
> Issue Type: Sub-task
> Components: SQL
> Reporter: Harshvardhan Gupta
> Assignee: Harshvardhan Gupta
> Attachments: explain.txt
>
>
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