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

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

> Andrew Dunstan <andrew(at)dunslane(dot)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