Re: "Cast" SRF returning record to a table type?

On Sat, Apr 18, 2015 at 5:37 PM, Jim Nasby <Jim.Nasby@bluetreble.com> wrote:
> On 4/18/15 12:47 AM, David G. Johnston wrote:
>>
>> If you could find a way to pass a value of type some_table into the
>> function - instead of the name/text 'some_table‘ - you could  possibly
>> use polymorphic pseudotypes...just imagining here...
>
>
> Oh, I didn't think about that. Maybe I'll try it.
>
> What I ended up with is this:
>
> CREATE FUNCTION ... (
> ) RETURNS SETOF text ...
> ...
> RETURN QUERY EXECUTE format(
>     'SELECT row(t.*)::text FROM %I.%I AS t'
>     , ...
> );
>
> So the function is getting a record and casting it to text. To call the
> function you have to...
>
> SELECT (function(...))::name_of_table).*

*do not do this*.  If table has three fields a,b,c, the query will expand to:

SELECT function(...).a, function(...).b, function(...).c;

SRF in column list (now that we have LATERAL) can now be considered a
'bad practice' in most cases I can think of (possibly exempting
trivial data productions with generate_series, etc).

> that gives you the same output as if you'd selected directly from the table.

I think the following is better:

postgres=# create table foo(id int, b text);
CREATE TABLE

postgres=# insert into foo select s, s || '_test' from generate_series(1,3) s;
INSERT 0 3

create or replace function getdata(r anyelement, tablename text)
returns setof anyelement as
$$
begin
  return query execute format('select * from %s', quote_ident(tablename));
end;
$$ language plpgsql;
CREATE FUNCTION

postgres=# select * from getdata(null::foo, 'foo');
  id │   b
────┼────────
  1 │ 1_test
  2 │ 2_test
  3 │ 3_test
(3 rows)

merlin