Re: Null comparison

On Wed, 13 Dec 2000, Al Lewis wrote:

> I am migrating to postgress from msql and am encountering numerous problems
> in the differences in NULL usage and comparison.
> 
> 1. Why are 2 fields not equal if they are both NULL?

Because that's what the SQL spec says.  If either value is NULL
the result is unknown (because NULL is not a value really,
is this unknown value equal to some other unknown value...).

> 2. Is there a way to easily modify my sql select statements to account for
> either column being NULL and having them return true if they both are NULL?
>     select a.name, b.cost from a, b where a.type=b.type

where a.type=b.type or (a.type is null and b.type is null)
should do it.

> I'd like to make this as easy as possible so I can put it into a
> "translation" function.  Currently I have a regsub that handles <> and
> NULLs, since <> doesn't work on a NULL field.