On 05/31/18 20:20, Charles Cui wrote:
> To clarify, I think my question is functions like json_each or
> json_object_keys() are
> set returning functions (
> https://www.postgresql.org/docs/9.5/static/functions-srf.html),
> which means it returns a set of results into a Datum.
Well, it returns one result row as a Datum (either a single value
or a tuple) each time it is called, until the whole set has been
returned. The process is described here
https://www.postgresql.org/docs/9.5/static/xfunc-c.html#XFUNC-C-RETURN-SET
(though that description is from the point of view of the set-returning
function being called, not the point of view of its caller).
-Chap