On Sep 12, 2023, at 21:00, Erik Wienhold <[email protected]> wrote:
>> I posted this question on Stack Overflow
>> (https://stackoverflow.com/q/77046554/79202),
>> and from the suggestion I got there, it seems that @@ expects a boolean to be
>> returned by the path query, while @? wraps it in an implicit exists(). Is
>> that
>> right?
>
> That's also my understanding. We had a discussion about the docs on @@, @?,
> and
> jsonb_path_query on -general a while back [1]. Maybe it's useful also.
Hi, finally getting back to this, still fiddling to figure out the differences.
From the thread you reference [1], is the point that @@ and jsonb_path_match()
can only be properly used with a JSON Path expression that’s a predicate check?
If so, as far as I can tell, only exists() around the entire path query, or the
deviation from the SQL standard that allows an expression to be a predicate?
This suggest to me that the "Only the first item of the result is taken into
account” bit from the docs may not be quite right. Consider this example:
david=# select jsonb_path_query('{"a":[false,true,false]}', '$.a ?(@[*] ==
false)');
jsonb_path_query
------------------
false
false
(2 rows)
david=# select jsonb_path_match('{"a":[false,true,false]}', '$.a ?(@[*] ==
false)');
ERROR: single boolean result is expected
jsonb_path_match(), it turns out, only wants a single result. But furthermore
perhaps the use of a filter predicate rather than a predicate expression for
the entire path query is an error?
Curiously, @@ seems okay with it:
david=# select '{"a":[false,true,false]}'@@ '$.a ?(@[*] == false)';
?column?
----------
t
Not a predicate query, and somehow returns true even though the first item of
the result is false? Is that how it should be?
Best,
David
[1]
https://www.postgresql.org/message-id/CACJufxE01sxgvtG4QEvRZPzs_roggsZeVvBSGpjM5tzE5hMCLA%40mail.gmail.com
