Re: string || NULL ambiguity

> On Wed, 2003-03-19 at 20:32, Oleg Bartunov wrote:
>> On Wed, 19 Mar 2003, Alvaro Herrera wrote:
>> > stringA||COALESCE(NULL, '')
>> >
>>
>> we don't know in advance if it's NULL or not.
>
> Right, that's the point of COALESCE: the first non-NULL argument is
> returned -- so if the first argument to COALESCE happens to be non-NULL,
> COALESCE has no effect.

I tried this with a txtidx column type:

tsearch=# select coalesce(NULL,'');case
------

(1 row)

tsearch=# select coalesce(NULL,'hi');case
------hi
(1 row)

tsearch=# select title_fts from article;           title_fts
----------------------------------'2':3A 'tsearch':1A 'version':2A'easi':1A 'implement':2A

(3 rows)

tsearch=# select coalesce('',title_fts) from article;
ERROR:  Void value
tsearch=# select coalesce('hi',title_fts) from article;case
------'hi''hi''hi'
(3 rows)

---

Note the error: "ERROR:  Void value" above.  Why is that happening?

--
Thomas