[gdal-dev] OGR SQL and lother dialects?

a.furieri at lqt.it a.furieri at lqt.it
Fri Dec 4 05:52:39 PST 2015

On Fri, 4 Dec 2015 14:29:47 +0100, Even Rouault wrote:
> So it looks very much like "x = NULL" is not "normal" SQL at all.

just a may be useful comment about this topic

accordingly to SQL standard syntax rules NULL should never be
confused with any other ordinary value; it's instead a special
marker denoting the absolute _absence_ of any value.
and consistently with this convention, any SQL operation or
comparison including a NULL term _should_ always return a
NULL result.

so an expression like "x = NULL" in pure SQL terms is just
a meaningless nonsense, because it will always evaluate to
a NULL constant.
the unique possible mechanism supported by standard SQL
allowing to check for NULL values is by using the special
comparison operators "x IS NULL" or "x IS NOT NULL"

bye Sandro

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