Postgres 12

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create table person (id integer, firstname varchar(10), lastname varchar(10));
insert into person values (1, 'Arthur', 'Dent'), (2, 'Ford', 'Prefect');

CREATE TABLE

INSERT 0 2

-- create a function that receives a complete row (record) from the table
-- and generates a full name display
create function full_name(p_row person)
returns text
as
$$
  select concat_ws(' ', p_row.firstname, p_row.lastname);
$$
language sql;

CREATE FUNCTION

select id, full_name(p)
from person p;

id
full_name

1
Arthur Dent

2
Ford Prefect

SELECT 2

-- change the function to use more columns
create or replace function full_name(p_row person)
returns text
as
$$
  select concat_ws(' ', p_row.firstname, p_row.lastname, concat('(', p_row.id, ')'));
$$
language sql;

CREATE FUNCTION

-- no change in calling the function
select id, full_name(p)
from person p;

id
full_name

1
Arthur Dent (1)

2
Ford Prefect (2)

SELECT 2