Re: table functions

Joe Conway <mail@joeconway.com> writes:
> This capability was added so late in the 7.3 developemnt cycle that I don't
> think it is documented anywhere other than the source code and some posts Tom
> Lane made to the list (although I'll have to look -- he may have snuck it in
> somewhere).

src/backend/utils/fmgr/README has

: If the function is being called as a table function (ie, it appears in a
: FROM item), then the expected tuple descriptor is passed in ReturnSetInfo;
: in other contexts the expectedDesc field will be NULL.  The function need
: not pay attention to expectedDesc, but it may be useful in special cases.

Someday that README should be rewritten and merged into the SGML
programmer's guide.  Right now, it's essential reading for backend
function authors.

            regards, tom lane