How to return a table by rowtype in PL/pgSQL

Question

I am trying to implement a function that returns a table with the same structure as an input table in the parameter, using PL/pgSQL (PostgreSQL 9.3). Basically, I want to update a table, and return a copy of the updated table with plpgsql. I searched around SO and found several related questions (e.g. Return dynamic table with unknown columns from PL/pgSQL function and Table name as a PostgreSQL function parameter), which lead to the following minimal test example:

CREATE OR REPLACE FUNCTION change_val(_lookup_tbl regclass)
RETURNS _lookup_tbl%rowtype AS --problem line
$func$
BEGIN
    RETURN QUERY EXECUTE format('UPDATE %s SET val = 2 RETURNING * ; ', _lookup_tbl);
END
$func$ LANGUAGE plpgsql;

But I can't get past giving the correct return type for TABLE or SETOF RECORD in the problem line. According to this answer:

SQL demands to know the return type at call time

But I think the return type (which I intend to borrow from the input table type) is known. Can some one help explain if it is possible to fix the signature of the above PL/pgSQL function?

Note, I need to parametrize the input table and return the update of that table. Alternatives are welcome.

Plane

Answer 1

What you have so far looks good. The missing ingredient: polymorphic types.

CREATE OR REPLACE FUNCTION change_val(_tbl_type anyelement)
  RETURNS SETOF anyelement  -- problem solved
  LANGUAGE plpgsql AS
$func$
BEGIN
   RETURN QUERY EXECUTE format(
      'UPDATE %s SET val = 2 RETURNING *;'
     , pg_typeof(_tbl_type))
     );
END
$func$;

Call (important):

SELECT * FROM change_val(NULL::some_tbl);

db<>fiddle here
_{Old sqlfiddle}

See (last paragraph):

• Refactor a PL/pgSQL function to return the output of various SELECT queries

Rutger

Thanks a lot! (esp. for the sqlfiddle:). – Plane

Is there any way i can call like SELECT * FROM change_val('some_tbl');???? – Jemison

@RamCh: No. The return type has to be declared at function declaration time. – Rutger