Re: [GENERAL] 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@gmail.com> writes:
>> On Sun, Dec 18, 2016 at 6:08 PM, John R Pierce <pierce@hogranch.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
>
>