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From "James Xu (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (BEAM-2255) support ORDER BY clause
Date Thu, 11 May 2017 15:56:04 GMT

    [ https://issues.apache.org/jira/browse/BEAM-2255?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16006669#comment-16006669
] 

James Xu commented on BEAM-2255:
--------------------------------

Just realised that `limit 10, 5` is implementable by using three nested `Top`:

1. first use Top to fetch (10 + 5) records
2. then use Top to strip the leading 10 records (the sorting order will be reversed)
3. use another Top to reverse the result of step two.



> support ORDER BY clause
> -----------------------
>
>                 Key: BEAM-2255
>                 URL: https://issues.apache.org/jira/browse/BEAM-2255
>             Project: Beam
>          Issue Type: New Feature
>          Components: dsl-sql
>            Reporter: James Xu
>            Assignee: James Xu
>
> Currently Beam does not have `global sort` support[1]. So we will implement a limited
version of `ORDER BY` using `org.apache.beam.sdk.transforms.Top` for now. So it will support
sql like:
> {code:sql}
> select * from t order by id desc limit 10;
> {code}
> but not support `ORDER BY` without a `limit`:
> {code:sql}
> select * from t order by id desc
> {code}
> and also not support `ORDER BY` with a `offset`:
> {code:sql}
> select * from t order by id desc limit 10, 10;
> {code}
> [1]. https://lists.apache.org/thread.html/bc0e65a3bb653b8fd0db96bcd4c9da5af71a71af5a5639a472167808@1464278191@%3Cdev.beam.apache.org%3E



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