Re: Bug in jsonb_path_exists (maybe _match) one-element scalar/variable jsonpath handling

On Fri, Dec 2, 2022 at 10:47 AM Alexander Korotkov <aekorotkov(at)gmail(dot)com>
wrote:

>
> > Thank you for explaining your point, but I can't agree with that.
> > Constant jsonpath expression is always returning item for the input
> > JSON value. Even despite the input value is ignored. This is
> > redundant case, but still correct.
>
> Let me explain more what I do mean. In the SQL SELECT statement there
> is a WHERE clause. This clause should express the predicate, which
> should match to rows. But you're writing "WHERE 1 = 1" or "WHERE
> true" then all rows are matching even that no column is referenced.
> This is how SQL is working. And I see no reason why jsonpath should
> work in a different way.
>
>
I like the analogy but it seems to support my conclusion moreso than yours:

Consider: select jsonb_path_exists('{"foo":"bar"}'::jsonb, 'false');

The analogous SQL query is: "SELECT * FROM table WHERE false" would
indeed produce an empty set - which EXISTS would interpret as false but you
want to evaluate to true

Or, "SELECT * FROM table WHERE 'banana';" which produces the same kind of
error that I wish jsonb_path_exists would produce when one writes a
similarly nonsensical path.

David J.

I'll probably get to a formal review of the patch - but actually I am
hoping someone else more comfortable in the codebase chimes in here with an
opinion. Though as I said, I'm willing to concede that the behavior should
probably stay unchanged, for compatibility reasons, and we just need to
decide on how to correctly document this.