Field value in a random PostgreSQL table record

random_field.sql

create table if not exists scientist (id integer primary key, firstname varchar(100), lastname varchar(100));
insert into scientist (id, firstname, lastname) values (1, 'albert', 'einstein') on conflict DO NOTHING;
insert into scientist (id, firstname, lastname) values (2, 'isaac', 'newton') on conflict DO NOTHING;
insert into scientist (id, firstname, lastname) values (3, 'marie', 'curie') on conflict DO NOTHING;


CREATE OR REPLACE FUNCTION random_record(
    table_name anycompatible
)
    RETURNS SETOF anycompatible
    LANGUAGE plpgsql
AS
'
DECLARE
    sql text := format($$
        SELECT * FROM %1$I
        ORDER BY random() LIMIT 1
    $$, pg_typeof(table_name));
BEGIN
    RETURN QUERY EXECUTE sql;
END
';

SELECT firstname FROM random_record(NULL::scientist);