Re: WIP json generation enhancements

On 11/26/2012 08:12 PM, Peter Eisentraut wrote:
> On 11/21/12 3:16 PM, Andrew Dunstan wrote:
>> One open question regarding this feature is whether this should return
>> NULL or '[]' for 0 rows. Currently it returns NULL but I could be
>> convinced to return '[]', and the change would be very small.
> Although my intuition would be [], the existing concatenation-like
> aggregates return null for no input rows, so this probably ought to be
> consistent with those.
>
In some previous mail Tom Lane claimed that by SQL standard
either an array of all NULLs or a record with all fields NULLs (I
don't remember which) is also considered NULL. If this is true,
then an empty array - which can be said to consist of nothing
but NULLs - should itself be NULL.

If this is so, than the existing behaviour of returning NULL in such
cases is what standard requires.

Hannu Krosing