Postgresql, jsonb_build_object and jsonb_agg

Question

Recently I have come across two queries as:

select jsonb_build_object('a', jsonb_agg(1))
 where false;

select jsonb_build_object('a', jsonb_agg(1))
 where false
having count(*) > 0;

First retuns {"a": null}, second - nothing, could you please explain me what happens in these 2 queries? I would expect nothing in result for BOTH.

Second query returns nothing because it filtered all records. If you have no records then result is nothing not null — Grzegorz Grabek
– Grzegorz Grabek, Commented Aug 27, 2018 at 7:11

Abelisto · Accepted Answer · 2018-08-27 09:37:35Z

2

It is not related to JSON functions.

select count(1) where false;

and

select count(1) where false having count(1) > 0;

providing same effect.

First query reporting that there is 0 records satisfied given condition in the where clause and in the second query having clause filtering out rows from the first query where count(1) <= 0

answered Aug 27, 2018 at 9:37

Abelisto

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