Re: Patch: Improve Boolean Predicate JSON Path Docs

On Jan 20, 2024, at 12:34, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:

> Surely we're not helping anybody by leaving that behavior in place.
> Making it do something useful, throwing an error, or returning NULL
> all seem superior to this. I observe that @@ returns NULL for the
> path type it doesn't like, so maybe that's what to do here.

I agree it would be far better for the behavior to be consistent, but frankly would like to see them raise an error. Ideally the hit would suggest the proper alternative operator or function to use, and maybe link to the docs that describe the difference between SQL-standard JSONPath and "predicate check expressions”, and how they have separate operators and functions.

I think of them as practically different data types (and wish they were, TBH). It makes sense that passing a JSON containment expression[1] would raise an error; so should passing the wrong flavor of JSONPath.

> BTW, jsonb_path_query_array and jsonb_path_query_first seem to
> take both types of path, like jsonb_path_query, so ISTM they need
> docs changes too.

Happy to update the patch, either to add those docs or, if we change the behavior to return a NULL or raise an error, then with that information, instead.

Best,

David

[1]: https://www.postgresql.org/docs/current/datatype-json.html#JSON-CONTAINMENT