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