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https://issues.apache.org/jira/browse/HIVE-3472?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13459301#comment-13459301
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Alan Gates commented on HIVE-3472:
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I read over the design doc but have not looked through the code on github yet.
The first question that comes to mind is why do you propose a separate parser
for this? I think many people will share your goal of making Hive SQL-92
compliant. But doing it with a totally separate parser underneath will cause
significant maintenance and usability issues. Bugs in one branch will not
match those in the other. Forcing users to think about whether they are in HQL
or SQL-92 will cause confusion and maintainability problems for them as well
(e.g. a .sql file written by user1 for HQL will be run in SQL-92 mode by user2,
producing either errors or wrong results).
Building one parser that can handle either would be a better approach for both
users and developers.
One other thought on open source process. It's often better to start with a
design doc or discussion on the dev lists before significant amounts of code
are contributed. This gives you a chance to get feedback early before you have
committed significant resources to a given path. Then code can be contributed
in small units that interested parties can review. The prospect of looking
through the thousands of lines of code in Hive to understand what is different
in panthera is daunting.
> Build An Analytical SQL Engine for MapReduce
> --------------------------------------------
>
> Key: HIVE-3472
> URL: https://issues.apache.org/jira/browse/HIVE-3472
> Project: Hive
> Issue Type: New Feature
> Affects Versions: 0.10.0
> Reporter: Shengsheng Huang
> Attachments: SQL-design.pdf
>
>
> While there are continuous efforts in extending Hive’s SQL support (e.g., see
> some recent examples such as HIVE-2005 and HIVE-2810), many widely used SQL
> constructs are still not supported in HiveQL, such as selecting from multiple
> tables, subquery in WHERE clauses, etc.
> We propose to build a SQL-92 full compatible engine (for MapReduce based
> analytical query processing) as an extension to Hive.
> The SQL frontend will co-exist with the HiveQL frontend; consequently, one
> can mix SQL and HiveQL statements in their queries (switching between HiveQL
> mode and SQL-92 mode using a “hive.ql.mode” parameter before each query
> statement). This way useful Hive extensions are still accessible to users.
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