[gdal-dev] OGR SQL and lother dialects?

[Jürgen E. Fischer]

Hi Even,

On Fri, 04. Dec 2015 at 14:29:47 +0100, Even Rouault wrote:
> Le vendredi 04 décembre 2015 14:08:40, Paolo Cavallini a écrit :
> > Hi all,
> > apparently the OGR SQL dialect is different from others:
> > https://hub.qgis.org/issues/7380
> > Any hope to bring them to common ground?

> I believe x = NULL is an extension of the SQL standard that may
> be supported or not by the various SQL engines.
> AFAIK, the SQL 92 standard only accepts the "x IS NULL" syntax.

> From my tests:
> 
> - SQLite rejects "x = NULL" syntax.

Not here.

SELECT 1 WHERE ''=NULL

returns no rows in sqlite3 - consistent with what I found in PostgreSQL and
Oracle (add "FROM dual" there).

> - OGR SQL accepts it (does not error on it), but it's more in the
> unspecified behaviour category and apparently doesn't behave like x IS NULL.
> I guess this must be evaluated like x = '' internally.

That might have been the original behaviour which caused the problem - but it
seems to have changed.

I found that OGR SQL (if that's still the default dialect) now behaves like the
others in that regard and x=NULL is different from x IS NULL.   I updated the
ticket accordingly.


Jürgen

-- 
Jürgen E. Fischer           norBIT GmbH             Tel. +49-4931-918175-31
Dipl.-Inf. (FH)             Rheinstraße 13          Fax. +49-4931-918175-50
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QGIS release manager (PSC)  Germany                    IRC: jef on FreeNode                         
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