How to split a type into multiple columns in Postgres?

Question

I have the following code to return multiple values from pl/python:

CREATE TYPE named_value AS (
  name   text,
  value  integer
);
CREATE or replace FUNCTION make_pair (name text, value integer)
  RETURNS named_value
AS $$
  return [ name, value ]
$$ LANGUAGE plpythonu;

select make_pair('egg', 4) as column;

The output is:

column
(egg,4)

What I want to do is to split the output into two separate columns. Like this:

column, column2
egg, 4

How do I do this? Googled for 1 hour got me nowhere. So I hope I will add some search keywords in the end: multiple return values multiple results multiple columns unnest list unnest set

Answer 1

Yeah, the syntax for this is a bit wacky, requiring extra parentheses:

select (make_pair('egg', 4)).name

To get multiple components from the output while only invoking the function once, you can use a sub-select:

select (x.column).name, (x.column).value from (select make_pair('egg', 4) as column) x;

Answer 2

The following is working code to avoid having to run the function twice and at the same time avoid a subquery.

CREATE TYPE named_value AS (
  name   text,
  value  integer
);

CREATE or replace FUNCTION setcustomvariable(variablename text, variablevalue named_value)
  RETURNS named_value
AS $$
  GD[variablename] = variablevalue
  return variablevalue
$$ LANGUAGE plpythonu;

CREATE or replace FUNCTION getcustomvariable(variablename text)
  RETURNS named_value
AS $$
  return GD[variablename]
$$ LANGUAGE plpythonu;

CREATE or replace FUNCTION make_pair (name text, value integer)
  RETURNS named_value
AS $$
  return [ name, value ]
$$ LANGUAGE plpythonu;

select setcustomvariable('result', make_pair('egg', 4)), (getcustomvariable('result')).name, (getcustomvariable('result')).value

Answer 3

A solution I found was to use join:

create table tmp (a int, b int, c int);
insert into tmp (a,b,c) values (1,2,3), (3,4,5), (5,12,13);
create type ispyth3 as (is_it boolean, perimeter int);
create function check_it(int, int, int) returns ispyth3 as $$
    begin
        return ($1*$1 + $2*$2 = $3*$3, $1+$2+$3);
    end
$$ language plpgsql;
select * from tmp join check_it(a,b,c) on 1=1;

This returns:

 a | b  | c  | is_it | perimeter 
---+----+----+-------+-----------
 1 |  2 |  3 | f     |         6
 3 |  4 |  5 | t     |        12
 5 | 12 | 13 | t     |        30
(3 rows)

Answer 4

SELECT * FROM make_pair('egg', 4);

and some variants:

 SELECT name, value FROM make_pair('egg', 4) AS x;


 SELECT a, b FROM make_pair('egg', 4) AS x(a,b);