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Re: Issue null-ordering

From: Elias Sinderson <elias@cse.ucsc.edu>
Date: Fri, 10 Jan 2003 09:18:01 -0800
Message-ID: <3E1F0049.2090001@cse.ucsc.edu>
CC: www-webdav-dasl@w3.org

Agreed, nulls should sort low. Given a DB that sorts high, it is a 
simple enough fix to move them to the low end.


Babich, Alan wrote:

>(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
>-----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
>  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
>  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,
><green/>bytes GmbH -- http://www.greenbytes.de -- tel:+492512807760
Received on Friday, 10 January 2003 12:18:49 UTC

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