Re: Concatenating NULL with JSONB value return NULL

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