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https://issues.apache.org/jira/browse/HIVE-835?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Carl Steinbach updated HIVE-835:
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Component/s: SQL
> Deprecate, remove, or fix MAP and REDUCE syntax.
> ------------------------------------------------
>
> Key: HIVE-835
> URL: https://issues.apache.org/jira/browse/HIVE-835
> Project: Hive
> Issue Type: Improvement
> Components: SQL
> Reporter: Adam Kramer
>
> There are syntactic elements MAP and REDUCE which function as syntactic sugar
> for SELECT TRANSFORM. This behavior is not at all intuitive, because no
> checking or verification is done to ensure that the user's intention is met.
> Specifically, Hive may see a MAP query and simply tack the transform script
> on to the end of a reduce job (so, the user says MAP but hive does a REDUCE),
> or (more dangerously) vice-versa. Given that Hive's whole point is to sit on
> top of a mapreduce framework and allow transformations in the mapper or
> reducer, it seems very inappropriate for Hive to ignore a clear command from
> the user to MAP or to REDUCE the data using a script, and then simply ignore
> it.
> Better behavior would be for hive to see a MAP command and to start a new
> mapreduce step and run the command in the mapper (even if it otherwise would
> be run in the reducer), and for REDUCE to begin a reduce step if necessary
> (so, tack the REDUCE script on to the end of a REDUCE job if the current
> system would do so, or if not, treat the 0th column as the reduce key, throw
> a warning saying this has been done, and force a reduce job).
> Acceptable behavior would be to throw an error or warning when the user's
> clearly-stated desire is going to be ignored. "Warning: User used MAP
> keyword, but transformation will occur in the reduce phase" / "Warning: User
> used REDUCE keyword, but did not specify DISTRIBUTE BY / CLUSTER BY column.
> Transformation will occur in the map phase."
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