>>>>> "Charles" == Charles Cui <charles.cui1984@gmail.com> writes:
Charles> Thanks you guys for answering my questions, and sorry for confusion.
Charles> To clarify, I think my question is functions like json_each or
Charles> json_object_keys() are
Charles> set returning functions (
Charles> https://www.postgresql.org/docs/9.5/static/functions-srf.html),
Charles> which means it returns a set of results into a Datum.
No. Set-returning functions follow a somewhat complex call protocol that
may involve the function being called multiple times (returning one row
each time as a composite Datum) or may involve the function being called
once and returning a tuplestore (not as the return value but via the
ReturnSetInfo struct).
I would not try calling a SRF directly from C code without going through
SPI (i.e. setting up and running an actual query from inside your
function).
I definitely think you should be looking at pg_parse_json instead.
--
Andrew (irc:RhodiumToad)