Re: coalesce(json_agg [..] filter where [..], '[]' in left join returning null

Thanks again David. I am very novice, and tried the following which does
not give an error but returns null instead of []
select
json_agg(
(select row_to_json(_) from
(select vc.id, vc.descr, vc.expense, vc.version,
vat_percentage) as _
)
)
from vat_cat vc
left join (
select
vatcat_id,
COALESCE(NULLIF(
json_agg(
(select row_to_json(_) from
(select vp.percentage, vp.version,
json_build_object(
'lower', lower(vp.validity),
'upper', upper(vp.validity),
'lower_inc', lower_inc(vp.validity),
'upper_inc', upper_inc(vp.validity)
) validity)
as _)
)::text,
'null'::text), '[]'::text) vat_percentage
from vat_percentage vp
group by vatcat_id

) vp on vc.id = vp.vatcat_id

On Wed, Jan 6, 2021 at 5:10 PM David G. Johnston <david(dot)g(dot)johnston(at)gmail(dot)com>
wrote:

> On Wed, Jan 6, 2021 at 8:59 AM Stefan Houtzager <
> stefan(dot)houtzager(at)gmail(dot)com> wrote:
>
>>
>> ERROR: operator does not exist: json = json LINE 11: COALESCE(NULLIF( ^
>> HINT: No operator matches the given name and argument types. You might need
>> to add explicit type casts. SQL state: 42883 Character: 306
>>
>>
> Right, json doesn't implement equality. You will need to cast to and
> compare text values.
>
> David J.
>
>

--
Kind regards,

Stefan Houtzager

Houtzager ICT consultancy & development

www.linkedin.com/in/stefanhoutzager