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RE: Issue null-ordering

From: Julian Reschke <julian.reschke@gmx.de>
Date: Thu, 9 Jan 2003 20:32:03 +0100
To: "Babich, Alan" <ABabich@filenet.com>, <www-webdav-dasl@w3.org>
Message-ID: <JIEGINCHMLABHJBIGKBCGEENGCAA.julian.reschke@gmx.de>

Thanks Alan,

suits me as well, as long as we can get the issue closed.

Julian

--
<green/>bytes GmbH -- http://www.greenbytes.de -- tel:+492512807760 

> -----Original Message-----
> From: www-webdav-dasl-request@w3.org
> [mailto:www-webdav-dasl-request@w3.org]On Behalf Of Babich, Alan
> Sent: Thursday, January 09, 2003 7:13 PM
> To: Julian Reschke; www-webdav-dasl@w3.org
> Subject: RE: Issue null-ordering
> 
> 
> 
> (1) Amelia is completely correct.
> (2) We MUST specify a definite ordering for nulls in the collation
> sequence if we ever hope to extend DASL in the future to
> cross-repository queries that do ordering. (Trust me, customers really
> want that.) Despite the fact that the SQL spec. caved in to one or more
> vendors who didn't want to change their implementation of where nulls
> sort, there is only one logical choice as to where null values sort --
> before all non-null values. That is because shorter strings always
> collate before longer strings, and zero length strings are the shortest
> strings of all. That is the way the DASL spec. is written.
> (3) The only imperfection in the spec is that, as Amelia says, the
> reason is inaccurate. So, to correct the imperfection, you might say
> something like the following:
> 
> "Nulls sort low, i.e., before all non null values. That is compatible
> with the SQL92 and SQL99 specs., and it is essential for a future
> extension for cross-repository searching."
> 
> Or, you could just say "That is compatible with the SQL92 and SQL99
> specs." for the reason.
> 
> Alan Babich
> 714-327-3403
> 
> -----Original Message-----
> From: Julian Reschke [mailto:julian.reschke@gmx.de] 
> Sent: Thursday, January 09, 2003 8:40 AM
> To: www-webdav-dasl@w3.org
> Subject: Issue null-ordering
> 
> 
> 
> A long time ago, Amelia Carlson wrote:
> 
>   In the WebDAV SEARCH spec (5.6, DAV:orderby), it says that nulls sort
> low, to match SQL92.
>   However, SQL92 and SQL99 both say "Whether a sort key value that is
> null is
>   considered greater or less than a non-null value is
> implementation-defined,
>   but all sort key values that are null shall either be considered
> greater than
>   all non-null values or be considered less than all non-null values."
>   (words taken from SQL99, 14.1 &lt;declare cursor&gt; General Rule
> 2)c), in
>   reference to null handling for the &lt;order by clause&gt;. )
>   I would note that in 5.5.3 WebDAV SEARCH says nulls are less than all
>   other values in a comparison, so the DAV:orderby matches that
> statement,
>   it just gives an inaccurate reason.
> 
> Seems to me that if SQL databases are free to decide where to sort NULL
> values (as long as they are consistent), we probably need to be just as
> flexible in DASL (otherwise we can't directly map to a SQL query).
> 
> Feedback appreciated,
> 
> 
> Julian
> 
> 
> <http://greenbytes.de/tech/webdav/draft-reschke-webdav-search-latest.htm
> l#rf
> c.issue.null-ordering>
> 
> --
> <green/>bytes GmbH -- http://www.greenbytes.de -- tel:+492512807760
> 
> 
> 
Received on Thursday, 9 January 2003 14:32:46 GMT

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