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From "Craig L Russell (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (JDO-721) Specifying NULL elements positioning in ordered columns
Date Fri, 17 May 2013 17:23:16 GMT

    [ https://issues.apache.org/jira/browse/JDO-721?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13660879#comment-13660879
] 

Craig L Russell commented on JDO-721:
-------------------------------------

I agree that it would be useful to have an extension to the OrderingSpec to allow nulls first
or nulls last per field to be ordered.

This could be implemented by many SQL standard databases by using NULLS FIRST or NULLS LAST;
or in MYSQL by using COALESCE, or IsNull(column) and isNotNull(column) as an ordering element.

Craig
                
> Specifying NULL elements positioning in ordered columns
> -------------------------------------------------------
>
>                 Key: JDO-721
>                 URL: https://issues.apache.org/jira/browse/JDO-721
>             Project: JDO
>          Issue Type: Improvement
>          Components: specification
>    Affects Versions: JDO 3 update 1 (3.0.1)
>            Reporter: Muhammad Gelbana
>            Priority: Minor
>              Labels: jdoql
>
> I don't know about other RDBMS but in MySQL ordering, it's possible to specify whether
NULL column fields are placed in the beginning or at the end of the ordering, i.e.:
> ORDER BY `values_column` IS NULL DESC
> [values_column]
> NULL
> NULL
> value1
> value2
> value3
> or the other way around (ORDER BY `values_column` IS NULL ASC):
> [values_column]
> value1
> value2
> value3
> NULL
> NULL
> I checked JDO 3 specification and found that JDOQL's ordering specification doesn't support
specifying NULL values handling:
> ------------------------------------------------------------------------------
> 26.7 Ordering Specification
> This section describes the syntax of the setOrdering argument.
>     OrderingClause:
>         OrderingSpecs ,opt
>     OrderingSpecs:
>         OrderingSpec
>         OrderingSpecs , OrderingSpec
>     OrderingSpec:
>         Expression Ascending
>         Expression Descending
>     Ascending: one of
>         asc ascending
>     Descending: one of
>         desc descending
> Please note, as a usability feature OrderingClause supports an optional trailing comma.
> ------------------------------------------------------------------------------
> Thank you for your time and efforts.

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