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https://issues.apache.org/jira/browse/HIVE-1096?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12892977#action_12892977
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Carl Steinbach commented on HIVE-1096:
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Notes from a design discussion on ##hive:
* Variables, configuration properties, system properties and environment
variables need to exist in separate namespaces.
* Variables should not be included in the hiveconf. They should only be
available/visible to the query pre-processor. In particular we do not want
variables to get passed over to the cluster.
* Add a '-hivevar' switch to the CLI for setting variables.
* Add a "var x=y" CommandProcessor for setting variables.
Here's an example of what we want:
{code}
var a="I am a variable"; -- ${a} == "I am a variable"
set a="I am a configuration property"; -- ${hiveconf:a} == "I am a
configuration property"
set prop1 = ${a}; -- ${hiveconf:prop1} == "I am a
variable"
set var1 = ${hiveconf:a}; -- ${var1} == "I am a configuration
property"
{code}
> Hive Variables
> --------------
>
> Key: HIVE-1096
> URL: https://issues.apache.org/jira/browse/HIVE-1096
> Project: Hadoop Hive
> Issue Type: New Feature
> Components: Query Processor
> Reporter: Edward Capriolo
> Assignee: Edward Capriolo
> Fix For: 0.6.0, 0.7.0
>
> Attachments: 1096-9.diff, hive-1096-10-patch.txt,
> hive-1096-11-patch.txt, hive-1096-12.patch.txt, hive-1096-2.diff,
> hive-1096-7.diff, hive-1096-8.diff, hive-1096.diff
>
>
> From mailing list:
> --Amazon Elastic MapReduce version of Hive seems to have a nice feature
> called "Variables." Basically you can define a variable via command-line
> while invoking hive with -d DT=2009-12-09 and then refer to the variable via
> ${DT} within the hive queries. This could be extremely useful. I can't seem
> to find this feature even on trunk. Is this feature currently anywhere in the
> roadmap?--
> This could be implemented in many places.
> A simple place to put this is
> in Driver.compile or Driver.run we can do string substitutions at that level,
> and further downstream need not be effected.
> There could be some benefits to doing this further downstream, parser,plan.
> but based on the simple needs we may not need to overthink this.
> I will get started on implementing in compile unless someone wants to discuss
> this more.
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