Michael Haeusler created HIVE-11022:
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Summary: 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 reduce
the amount of data transferred to reducers.
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