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https://issues.apache.org/jira/browse/HIVE-416?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12700013#action_12700013
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Zheng Shao commented on HIVE-416:
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@Raghu: I just had a second thought on that approach. The new production you
add is left-recursive and it's not permitted in LL(k), but it's possible to use
precedence rules to fix that.
However given all the change including the flattening, it seems to me that's
too much work with very little benefit - who care about the optional brackets,
for usage it's exactly the same.
For Venky's case, it's a separate problem. Venky's case is more like supporting
"a" and "((((a))))". We should be able to support it easily once we allow
omitting the sub query alias.
> Get rid of backtrack in Hive.g
> ------------------------------
>
> Key: HIVE-416
> URL: https://issues.apache.org/jira/browse/HIVE-416
> Project: Hadoop Hive
> Issue Type: Improvement
> Components: Query Processor
> Affects Versions: 0.4.0
> Reporter: Zheng Shao
> Assignee: Zheng Shao
> Fix For: 0.4.0
>
> Attachments: HIVE-416.1.1.patch, HIVE-416.1.patch
>
>
> Hive.g now still uses "backtrack=true". "backtrack" not only slows down the
> parsing in case of error, it can also produce wrong syntax error messages
> (usually based on the last try of the backtracking).
> We should follow
> http://www.antlr.org/wiki/display/ANTLR3/How+to+remove+global+backtracking+from+your+grammar
> to remove the need of doing backtrack.
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