Re: Concat error in PL/pgsql

I don't have a bug template at hand.

Within a plpgsql function, concatenating TEXT strings from tables that allow NULL values return nil results. Please run the following. The result of the second select is nil.

Cheers, H.P.

-----------------------------------------------------------

create table tconcattest (id char(3),str text);

insert into tconcattest values('hpw',text('Something...'));
insert into tconcattest values('wuh',text('and more of something.'));

create function fconcattest () returns text as'
declare
r record;
output text;
begin
output := text('''');
for r in select * from tconcattest loop
output := output || r.str;
end loop;
return output;
end;
' language 'plpgsql';

select fconcattest();

insert into tconcattest values('abc',NULL);

select fconcattest();

update tconcattest set str='...again' where id='abc';

select fconcattest();

Hans Peter Wuermli <wurmli(at)freesurf(dot)ch> writes:
> Within a plpgsql function, concatenating TEXT strings from tables that
> allow NULL values return nil results.

That's not a bug: NULL concatenated with anything produces NULL,
per SQL92 specification.

If you want a NULL to act like an empty string, try

for r in select * from tconcattest loop
output := output || coalesce(r.str, '''');

regards, tom lane

Simple add lines as shown:

> for r in select * from tconcattest loop
IF r.str IS NOT NULL THEN
> output := output || r.str;
END IF;
> end loop;

- Andrew

A few hours ago, I wrote:
>
> Simple add lines as shown:
>
> > for r in select * from tconcattest loop
> IF r.str IS NOT NULL THEN
> > output := output || r.str;
> END IF;
> > end loop;
>

This would probably be better:

for r in select * from tconcattest where str is not null loop
output := output || r.str;
end loop;