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From "Carl Steinbach (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HIVE-1096) Hive Variables
Date Fri, 19 Feb 2010 03:26:28 GMT

    [ https://issues.apache.org/jira/browse/HIVE-1096?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12835566#action_12835566

Carl Steinbach commented on HIVE-1096:

bq. Where does the ${VARNAME} syntax come from? SCOPE uses @@VARNAME for their syntax for
a somewhat similar feature. Just curious.

Unix shell command interpreters, Perl, Make, Ant, Eclipse, [Amazon's EMR version of Hive |http://developer.amazonwebservices.com/connect/entry.jspa?externalID=2856]
and many templating systems (which is basically what this is) use the unary operator $ for
string substitution. Eclipse also defines various namespaces, so for example it is possible
to reference environment variables as ${env_var:HOME} and system properties as ${system_property:java.home}.
MySQL and T-SQL both use @ to identify user variables, and @@ to identify system variables
(see http://dev.mysql.com/doc/refman/5.0/en/user-variables.html), which was probably the inspiration
for SCOPE's syntax. SQL*Plus apparently uses '&'. 

> Hive Variables
> --------------
>                 Key: HIVE-1096
>                 URL: https://issues.apache.org/jira/browse/HIVE-1096
>             Project: Hadoop Hive
>          Issue Type: New Feature
>            Reporter: Edward Capriolo
>            Assignee: Edward Capriolo
>         Attachments: 1096-9.diff, hive-1096-2.diff, hive-1096-7.diff, hive-1096-8.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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