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From "Carl Steinbach (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HIVE-1096) Hive Variables
Date Tue, 27 Jul 2010 23:07:17 GMT

    [ https://issues.apache.org/jira/browse/HIVE-1096?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12892977#action_12892977
] 

Carl Steinbach commented on HIVE-1096:
--------------------------------------

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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