How to return a single composite type from a plpgsql function without repeating the composite type's parts explicitly as OUT parameters?

Question

I've hunted online and through documentation, but the much more common use case appears to be returning a SETOF some particular row type, not just a single row.

The use case below is trivial for illustration, as I am just trying to determine if this is even possible in plpgsql, and understand the syntax to use for it if it is. (Just like the Postgresql documentation contains examples of functions to return a static set of fixed values, the point here is not the use case but the syntax.)

With this table:

create table my_table (f1 int primary key, f2 text, f3 real, f4 text, f5 bool);

The following function can be created:

create function my_func1(f1_to_look_up int) returns my_table
language sql
as $$ select * from my_table where f1 = f1_to_look_up $$;

Also, this can be done in plpgsql like so, with explicit out parameters (and with f1 specified explicitly in the where clause to avoid ambiguity):

create function my_func2(f1_to_look_up int, out f1 int, out f2 text, out f3 real, out f4 text, out f5 bool)
language plpgsql
as $$
begin
  select * into strict f1, f2, f3, f4, f5
    from my_table where my_table.f1 = f1_to_look_up;
  return;
end
$$;

Is there a way to accomplish the same thing in plpgsql, without needing to repeat the definition of my_table in order to list all the OUT parameters?

Answer 1

You can return a row type by using an expression with that type. here it's effectively select my_table from my_table

create function my_func4(f1_to_look_up int) returns my_table language plpgsql
as $$
    begin
        return my_table from my_table where f1 = f1_to_look_up;
    end; 
$$;

or via a variable

create or replace function my_func4(f1_to_look_up int) returns my_table language plpgsql
as $$
    declare
        retval my_table;
    begin
        select into retval * from my_table where f1 = f1_to_look_up;
        return retval;
    end; 
$$;

---

You can also use a row constructor, which would be especially useful if the query is more complicated and you need to return values taken from more than one table joined together:

create function my_func5(f1_to_look_up integer)
 returns my_table
 language plpgsql
as $function$
begin
  return row(t.*) from my_table as t where f1 = f1_to_look_up;
end
$function$
;

The key is that where the plpgsql syntax documentation indicates that you can write return expression, "expression" can be everything that would ordinarily follow "select" in a normal SQL query.

Answer 2

I figured it out while writing the question; so far as I can tell this is the only way to do it:

create function my_func3(f1_to_look_up int, out my_result my_table)
language plpgsql
as $$
begin
  select * into strict my_result from my_table where f1 = f1_to_look_up;
  return;
end
$$;