Re: CAST(null as date)...

On Tue, 18 Jun 2002, Ian Harding wrote:

> I tried to create a function to return the string 'null' (without
> quotes, of course...) if the input was a zero length string, so I
> could use it in casting arguments to another function such as:
>
> select myfunction(cast(nullifzls($maybeemptyvar) as date),
> cast(....));
>
> However I have this dilemma.  The return type from the nullifzls
> function is text.  Text blows up the cast.  Is there any way to make
> this work, or should I do something else?

Wouldn't you want the function to return NULL, not 'null' since
the latter is a perfectly happily defined string containing the
word null? ;)

create function ff(text) returns text as 'select case when $1 = '''' then
cast(NULL as text) else $1 end;' language 'sql';

sszabo=# select ff('');
 ff
----

(1 row)

sszabo=# select cast (ff('') as date);
 ff
----

(1 row)

sszabo=# select cast (ff('') as date) is NULL;
 ?column?
----------
 t
(1 row)