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https://issues.apache.org/jira/browse/IMPALA-9962?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Work on IMPALA-9962 started by Gabor Kaszab.
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> Implement ds_kll_quantiles() function
> -------------------------------------
>
> Key: IMPALA-9962
> URL: https://issues.apache.org/jira/browse/IMPALA-9962
> Project: IMPALA
> Issue Type: Improvement
> Components: Backend
> Reporter: Gabor Kaszab
> Assignee: Gabor Kaszab
> Priority: Major
>
> Requirements for ds_kll_quantiles()
> - Receives a serialized KLL sketch in BINARY type (in Impala it can be
> STRING as long as we don't have BINARY) as first parameter.
> - Receives one or more double values to represent the quantile points.
> - In Hive the return type is an array of doubles. However, Impala can't
> return complex types from functions at this point so we have to find some
> alternative approaches to implement this function.
> ** One would be to return as many columns as many quantile points were given.
> ** Another approach is to create a comma separated string from the results
> of this function and return that string instead of an array.
> Hive example:
> {code:java}
> select ds_kll_quantiles(ds_kll_sketch(cast(int_col as float)), 0, 0.1, 0.5,
> 1) from table_name
> +--------------------+
> | _c0 |
> +--------------------+
> | [1.0,1.0,1.0,1.0] |
> +--------------------+
> {code}
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