Question

I have dynamicly generated SELECT. I try to return result as SETOF RECORD. Sth like that:

CREATE FUNCTION test(column_name text) RETURNS SETOF RECORD AS $$
DECLARE
   row  RECORD;
BEGIN
   FOR row IN EXECUTE 'SELECT ' || quote_ident(column_name) || ' FROM dates'
LOOP
   RETURN NEXT row;
END LOOP;
RETURN;
END;
$$ LANGUAGE 'plpgsql';

When I try:

SELECT * FROM test('column1');

I get this:

ERROR:  a column definition list is required for functions returning "record"

I know that column1 is integer type:

SELECT * FROM test('column1') f(a int);

result is correct, because I know that this is going to be Integer type.

When I try:

SELECT * FROM test('column1') f(a varchar);

I get error:

ERROR:  wrong record type supplied in RETURN NEXT
DETAIL:  Returned type integer does not match expected type character varying in column 1.

Now my question:
What to do to get rid of part of querty where I define types ‘f(a int)’. It should by feasible because Postgres knowns what is returned type. I tried with IMMUTABLE options, but unsuccessfully.

Answer 1

You could cast the value to text inside the function, and declare that the function RETURNS SETOF text. You can also return the whole result set at once; no need to iterate explicitly.

CREATE TABLE dates (column1 int, column2 date);
INSERT INTO dates VALUES (1, date '2012-12-22'), (2, date '2013-01-01');

CREATE FUNCTION test(column_name text) RETURNS SETOF text AS $$
BEGIN
   RETURN QUERY EXECUTE 'SELECT '
      || quote_ident(column_name) || '::text FROM dates';
END;
$$ LANGUAGE 'plpgsql';

Now SELECT test('column1'); yields:

 test 
------
 1
 2
(2 rows)

… and (with my locale settings) SELECT test('column2'); yields:

    test    
------------
 2012-12-22
 2013-01-01
(2 rows)