postgres=# create table tb1(id integer,name character varying);
CREATE TABLE
postgres=# 
postgres=# insert into tb1 select generate_series(1,5),'aa';
INSERT 0 5 

create or replace function func01()returns setof character varying as $$
declare
n character varying;
begin
 for i in 1..5 loop
 select name into n from tb1 where id=i;
 return next n;
 end loop;
end
$$ language plpgsql;

create or replace function func02(out character varying)returns setof character varying as $$
begin
 for i in 1..5 loop
 select name into $1from tb1 where id=i;
 return next;
 end loop;
end
$$ language plpgsql;

create or replace function func03()returns setof character varying as $$
begin
 for i in 1..5 loop
 return query(select name from tb1 where id=i);
 end loop;
end
$$language plpgsql;

create or replace function func04()RETURNS SETOF RECORD as $$
declare
 r record;
begin
 for i in 1..5 loop
 select * into r from tb1 where id=i;
 return next r;
 end loop;
end;
$$language plpgsql;

postgres=# select func04();
ERROR: set-valued function called in context that cannot accept a set
CONTEXT: PL/pgSQL function func04() line 7 at RETURN NEXT

If you call your set-returning function the wrong way (IOW the way you might normally call a function), you will get this error message: Set-valued function called in context that cannot accept a set. Incorrect: select sr_func(arg1, arg2, …); Correct: select * from sr_func(arg1, arg2, …);

postgres=# select * from func04();
ERROR: a column definition list is required for functions returning "record"
LINE 1: select * from func04();

postgres=# select * from func04() as t(id integer,name character varying);
 id | name 
----+------
 1 | aa
 2 | aa
 3 | aa
 4 | aa
 5 | aa
(5 rows)

create or replace function func05(out out_id integer,out out_name character varying)returns setof record as $$
declare
 r record;
begin
 for i in 1..5 loop
 select * into r from tb1 where id=i;
 out_id:=r.id;
 out_name:=r.name;
 return next;
 end loop;
end;
$$language plpgsql;

postgres=# select * from func05();
 id | name 
----+------
 1 | aa
 2 | aa
 3 | aa
 4 | aa
 5 | aa
(5 rows)

create or replace function func06()returns setof record as $$
begin
 for i in 1..5 loop
 return query(select id,name from tb1 where id=i);
 end loop;
end;
$$language plpgsql;

postgres=# select * from func06() as t(id integer,name character varying);
 id | name 
----+------
 1 | aa
 2 | aa
 3 | aa
 4 | aa
 5 | aa
(5 rows)

mytest=# create or replace function test_0830_5() returns setof test
mytest-# as $$
mytest$# DECLARE
mytest$# r test%rowtype; -- 将
mytest$# BEGIN
mytest$# FOR r IN
mytest$# SELECT * FROM test WHERE id > 0
mytest$# LOOP
mytest$# RETURN NEXT r;
mytest$# END LOOP;
mytest$# RETURN;
mytest$# END
mytest$# $$ language plpgsql;
CREATE FUNCTION
 
mytest=# select test_0830_5(1);
test_0830_5
------------------------------------------
(2,abcabc,"2018-08-30 09:26:14.392187")
......
(11,abcabc,"2018-08-30 09:26:14.392187")
(10 rows)
 
mytest=# select * from test_0830_5();
id | col1 | col2
----+--------+----------------------------
2 | abcabc | 2018-08-30 09:26:14.392187
......
11 | abcabc | 2018-08-30 09:26:14.392187
(10 rows)

mytest=# CREATE OR REPLACE FUNCTION test_0830_6(date) RETURNS SETOF integer AS $$
mytest$# BEGIN
mytest$# RETURN QUERY SELECT id
mytest$# FROM test
mytest$# WHERE col2 >= $1
mytest$# AND col2 < ($1 + 1);
mytest$# IF NOT FOUND THEN
mytest$# RAISE EXCEPTION 'No id at %.', $1;
mytest$# END IF;
mytest$# RETURN;
mytest$# END
mytest$# $$
mytest-# LANGUAGE plpgsql;
CREATE FUNCTION
mytest=# select test_0830_6('2018-08-30');
test_0830_6
-------------
2
......
11
(10 rows)