Re: to_json(NULL) should to return JSON null instead NULL

On Sat, Aug 29, 2015 at 3:39 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:

Andrew Dunstan <andrew@dunslane.net> writes:
> On 08/29/2015 08:47 AM, Shulgin, Oleksandr wrote:
>> Given there were no loud complaints about this, the current behavior
>> is appropriate for most users, the rest can still work around using
>> coalesce(to_json(...), json 'null').

> I don't think it's necessarily more correct. But I do agree that it's
> not a good idea to change the behaviour unless there is major
> unhappiness with it.

I'm not entirely convinced that JSON NULL and SQL NULL should be treated
as the same concept, so I would say that the current behavior is fine ---
at least when you think about it in isolation.  However, haven't we
already bought into that equivalence in these examples?

regression=# select row_to_json(row(1,null,2));
        row_to_json
---------------------------
 {"f1":1,"f2":null,"f3":2}
(1 row)

regression=# select array_to_json(array[1,null,2]);
 array_to_json
---------------
 [1,null,2]
(1 row)

or even in to_json itself:

regression=# select to_json(array[1,null,2]);
  to_json
------------
 [1,null,2]
(1 row)

The scalar case is definitely failing to be consistent with these.

Yes, that's my argument for correctness also: to_json() on a composite object should behave like distribution of to_json() calls over object/array elements.

 

Is consistency a sufficient reason to change it?

Not for me.

--

Alex