Re: Concatenating NULL with JSONB value return NULL

Thanks Tom, Melvin, and John!

@John, I keep forgetting the semantic differences between my programming
language and PostgreSQL.

I will go for Tom's COALESCE than Melvin's, purely for less typing.

Thanks again, all!

- Jong-won

On 19/12/16 11:46, Tom Lane wrote:
> Melvin Davidson <melvin6925(at)gmail(dot)com> writes:
>> On Sun, Dec 18, 2016 at 6:08 PM, John R Pierce <pierce(at)hogranch(dot)com> wrote:
>>> On 12/18/2016 2:52 PM, Jong-won Choi wrote:
>>>> I have a NULL-able JSONB type column and want to perform upsert,
>>>> concatenating with the existing value.
>>> NULL does not mean 'NO' value in SQL it means UNKNOWN value. sort of like
>>> the 'indeterminate' in math.
>> Have you tried using CASE?
>> INSERT INTO Fan (oid, campaigns, facts) VALUES (189,'{"campaign-id":
>> "12345"}','{"attended": false}')
>> ON CONFLICT (oid)
>> DO UPDATE SET campaigns = EXCLUDED.campaigns,
>> CASE WHEN fan.facts is NULL
>> THEN facts = EXCLUDED.facts
>> ELSE facts = fan.facts || EXCLUDED.facts
>> END
>> RETURNING *;
> Another option is COALESCE:
>
> ...
> DO UPDATE SET campaigns = EXCLUDED.campaigns,
> facts = COALESCE(fan.facts, '{}'::jsonb) || EXCLUDED.facts
> ...
>
> I'd argue though that if you think this is okay, then you're abusing
> NULL; that's supposed to mean "unknown", not "known to be empty".
> It would be better to initialize the column to '{}' to begin with.
>
> regards, tom lane
>
>