Re: SQL/JSON path issues/questions

On Tue, 16 Jul 2019 at 19:44, Alexander Korotkov
<a.korotkov@postgrespro.ru> wrote:
>
> On Tue, Jul 16, 2019 at 9:22 PM Thom Brown <thom@linux.com> wrote:
> > Now I'm looking at the @? and @@ operators, and getting a bit
> > confused.  This following query returns true, but I can't determine
> > why:
> >
> > # SELECT '{"a":[1,2,3,4,5]}'::jsonb @? '$.b == "hello"'::jsonpath;
> >  ?column?
> > ----------
> >  t
> > (1 row)
> >
> > "b" is not a valid item, so there should be no match.  Perhaps it's my
> > misunderstanding of how these operators are supposed to work, but the
> > documentation is quite terse on the behaviour.
>
> So, the result of jsonpath evaluation is single value "false".
>
> # SELECT jsonb_path_query_array('{"a":[1,2,3,4,5]}'::jsonb, '$.b == "hello"');
>  jsonb_path_query_array
> ------------------------
>  [false]
> (1 row)
>
> @@ operator checks that result is "true".  This is why it returns "false".
>
> @? operator checks if result is not empty.  So, it's single "false"
> value, not empty list.  This is why it returns "true".
>
> Perhaps, we need to clarify this in docs providing more explanation.

Understood.  Thanks.

Also, is there a reason why jsonb_path_query doesn't have an operator analog?

Thom