Re: [HACKERS] Error calling PG_RETURN_NULL()

[ Moved to pgsql-general. pgsql-hackers is for development of PostgreSQL
itself. ]

On Mon, 2011-07-25 at 20:06 -0300, Alexandre Savaris wrote:
> ********** Error **********
>
> ERRO: input function 49344 returned NULL
> SQL state: XX000
> Character: 45
>
> It seems like the call to PG_RETURN_NULL() on the input function is
> causing the error. Is this the correct behaviour? There's another way to
> return a NULL value as the result of a data type's input function?

The docs say:

"The input function must return a value of the data type itself."

http://www.postgresql.org/docs/9.0/static/sql-createtype.html

Which means you can't return a NULL from the input function when there
is non-NULL input. The context around that statement is a little more
informative, but perhaps it could be more clear.

I assume that postgresql has that requirement because it needs to know
whether something is NULL without necessarily knowing what type it is.
For instance:
' ' IS NULL
Should that be true or false? If it depends on the type of the
left-hand-side, how do you figure out what type it is? I'm not sure if
this is the exact reason it's prohibited, but it seems like there would
be a problem somewhere along these lines.

Interesting idea though.

Regards,
Jeff Davis