Re: NULL values and string

Sergey Karin wrote:
> Hi, List!
>
> I'm using PG8.1.
>
> Are there any abilities to represent NULL values as string?

Null isn't a real value. Try not to think of it as a value.

http://archives.postgresql.org/pgsql-sql/2003-01/msg00222.php

>     num_value alias for $1;

>    string_value := \'input value = \' || num_value;

> If I einvoke my function with NULL argument, it return NULL. But I want
> 'input value = NULL'.

Because NULL means unknown. A string with an unknown string appended to
it is itself unknown.

> Of course, I can check input value like this:
>
> if(num_value isnull) then
>    string_value := \'input value = NULL\';
> else
>    string_value := \'input_value = \' || num_value;
> end if;
>
> But it is not laconic...

Try something like:
   string_value := ''input_value = '' || COALESCE(num_value, 'a null');

--
   Richard Huxton
   Archonet Ltd