Postgres 15

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CREATE TABLE amp_pumpstations (
  inservice int
);

insert into amp_pumpstations values
(2010),
(2019),
(2000),
(1900);

CREATE TABLE

INSERT 0 4

select extract (year from current_date)::int - inservice 
from amp_pumpstations;

?column?

13

4

23

123

SELECT 4

CREATE OR REPLACE FUNCTION get_age()
RETURNS SETOF integer
AS $CODE$
BEGIN
    RETURN QUERY select extract (year from current_date)::int - inservice 
    from amp_pumpstations;
    
End
$CODE$
LANGUAGE PLPGSQL IMMUTABLE

CREATE FUNCTION

select *
from get_age()

get_age

13

4

23

123

SELECT 4