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)
