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From "Dag H. Wanvik (JIRA)" <j...@apache.org>
Subject [jira] Commented: (DERBY-4079) Add support for SQL:2008 <result offset clause> and <fetch first clause> to limit result set cardinality
Date Tue, 03 Mar 2009 15:12:57 GMT

    [ https://issues.apache.org/jira/browse/DERBY-4079?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12678342#action_12678342
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Dag H. Wanvik commented on DERBY-4079:
--------------------------------------

Thanks for looking at this, Knut. You are right, there as many aspects
of the efficiency calculations here, so it is probably better to avoid
getting into details here (some stuff could go into the tuning manual
perhaps). As for the materialization point; i was thinking of the case
where the app fetches the entire result set. In the client/server
case, the benefits from avoiding shipping all rows over the wire could
in deed be important, too.

I will post a preliminary patch in day day or two; I have one that
seems to work in my sandbox, but I need to clean it up a little first.


> Add support for SQL:2008 <result offset clause> and <fetch first clause>
to limit result set cardinality
> --------------------------------------------------------------------------------------------------------
>
>                 Key: DERBY-4079
>                 URL: https://issues.apache.org/jira/browse/DERBY-4079
>             Project: Derby
>          Issue Type: New Feature
>          Components: SQL
>            Reporter: Dag H. Wanvik
>            Assignee: Dag H. Wanvik
>         Attachments: ref.zip
>
>
> SQL 2008 has added new syntax to support a direct way to limit the
> returned set of rows in a result set.  This allows an application to
> retrieve only some rows of an otherwise larger result set, similar to
> the popular LIMIT clauses use in some databases.
> Up till now, in Derby (and SQL) we have had to use the ROW_NUMBER()
> function in a nested subquery to achieve the effect of the <fetch
> first clause>, cf. DERBY-2998, a method which is rather more indirect
> and still not efficient (DERBY-3505), and primarily intended for OLAP
> functionality, perhaps.
> There has been no direct way to achieve the effect of the <result
> offset clause> via SQL.
> Syntax (cf. SQL 2008, section 7.13):
>        <result offset clause> ::= OFFSET <n> {ROW | ROWS}
>        <fetch first clause> ::=      FETCH {FIRST | NEXT} [<n>] {ROW | ROWS}
ONLY
> where <n> is an integer. The two clauses syntactically follow the ORDER BY
> clause in the grammar.
> Note that both ORDER BY and the new clauses above are allowed also in
> subqueries in the new version of the SQL standard (section 7.13). I
> only propose to include this at the top level in DERBY for now. (ORDER
> BY is presently also not allowed in subqueries in Derby since SQL
> didn't allow for this until SQL 2008 either).

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