[Qgis-user] Query expression bugs with NULL Values

[Andre Joost]

Am 25.03.2015 um 20:07 schrieb José Carlos Martínez Llario:

>
>
> The layers has 48 NULL values,


...

> THIS IS OK
> "amenity" is not NULL returns 48
> "amenity" is NULL returns  4587
>

This does not make nuch sense to me. Do you have 48 empty (NULL) 
entries, or 48 non-empty values?

> THIS IS WRONG (if null values can not be treated as a text in the syntax
> it shouldnt work in both cases or throw some error)
> "amenity" <> 'NULL' returns 48
> "amenity"  =  'NULL'  returns 0   ????

No, NULL and 'NULL' are two different things. It is possible to write 
'NULL' as a text value for amenity (although it does not make sense, but 
the OSM database does not reject it).

So it should be ok that "amenity"  =  'NULL' returns nothing in your 
dataset.

HTH,
André Joost