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https://issues.apache.org/jira/browse/TAJO-87?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13722120#comment-13722120
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Hyunsik Choi commented on TAJO-87:
----------------------------------

Jinho,

I know your elegant error handling code in the old parser. But, the API of 
Antlr4 is incompatible to that of Antlr3. Actually, I need more time in order 
to implement the same feature because I have to survey Antlr4's error handling. 
If you are willing to port the error handling code from the old parser to the 
new parser, I really appreciate you.
                
> Integration of tajo algebra module and SQL parser.
> --------------------------------------------------
>
>                 Key: TAJO-87
>                 URL: https://issues.apache.org/jira/browse/TAJO-87
>             Project: Tajo
>          Issue Type: Improvement
>          Components: parser
>            Reporter: Hyunsik Choi
>            Assignee: Hyunsik Choi
>             Fix For: 0.2-incubating
>
>         Attachments: TAJO-87.patch
>
>
> In the current implementation, QueryAnalyzer transforms a sql statement into 
> a data structure that represents a parser tree and a query block. They has 
> the following limitations: 
>  * They can't support multiple block queries including table and scalar 
> subqueries. 
>  * They are tightly coupled to a certain grammar.
> Before ASF incubation, I have developed tajo-algebra and tajo-frontend-sql. 
> Tajo-algebra is a kind of intermediate layer. It represents a just relational 
> algebraic expression. With this, we can do more interesting things. For 
> example, we can enable users to describe a logical plan for a certain query. 
> It also very helpful to support an another DSL.
> For this work, tajo-algebra should be improved to support full 
> specifications, and we should rewrite a SQL parser to use tajo-algebra.

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