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https://issues.apache.org/jira/browse/HIVE-416?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12699873#action_12699873
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Ashish Thusoo commented on HIVE-416:
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I think for Identifier DOT Identifier we should probably treat it as a lexical
rule rather than a grammar rule. It will also make it much simpler to support
optional aliasing with complex types.
Right now
select T.a.b FROM T
and
select a.b FROM T
is very hard to handle in the SemanticAnalyzer as the grammar treats a as a
table alias instead of a complex column name.
About the comment on optional brackets - clearly these are optional in
expressions. So how do we support those expression e.g (a+b) and a+b are both
valid sql expressoins if we cannot support this without backtracking...
> 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.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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