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https://issues.apache.org/jira/browse/HIVE-11022?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Michael Haeusler updated HIVE-11022:
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Description:
Hive currently supports aggregation of lists "in order of input rows" with the
UDF collect_list. Unfortunately, the order is not well defined when map-side
aggregations are used.
Hive could support collecting lists in user-defined order by providing a UDF
COLLECT_LIST_SORTED(valueColumn, sortColumn[, limit]), that would return a list
of values sorted in a user defined order. An optional limit parameter can
restrict this to the n first values within that order.
Especially in the limit case, this can be efficiently pre-aggregated and
reduces the amount of data transferred to reducers.
was:
Hive currently supports aggregation of lists "in order of input rows" with the
UDF collect_list. Unfortunately, the order is not well defined when map-side
aggregations are used.
Hive could support collecting lists in user-defined order by providing a UDF
COLLECT_LIST_SORTED(valueColumn, sortColumn[, limit]), that would return a list
of values sorted in a user defined order. An optional limit parameter can
restrict this to the n first values within that order.
Especially in the limit case, this can be efficiently pre-aggregated and reduce
the amount of data transferred to reducers.
> Support collecting lists in user defined order
> ----------------------------------------------
>
> Key: HIVE-11022
> URL: https://issues.apache.org/jira/browse/HIVE-11022
> Project: Hive
> Issue Type: New Feature
> Components: UDF
> Reporter: Michael Haeusler
>
> Hive currently supports aggregation of lists "in order of input rows" with
> the UDF collect_list. Unfortunately, the order is not well defined when
> map-side aggregations are used.
> Hive could support collecting lists in user-defined order by providing a UDF
> COLLECT_LIST_SORTED(valueColumn, sortColumn[, limit]), that would return a
> list of values sorted in a user defined order. An optional limit parameter
> can restrict this to the n first values within that order.
> Especially in the limit case, this can be efficiently pre-aggregated and
> reduces the amount of data transferred to reducers.
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