schema_scope.sql

drop schema if exists a cascade;
create schema a;

drop schema if exists b cascade;
create schema b;

create table b.things (id int);
insert into b.things (id) values (1);
insert into b.things (id) values (2);
insert into b.things (id) values (3);

set search_path=a;

create table things (id int);
create function sum_things() returns bigint as
$$
  select sum(id) from things;
$$ language sql;
select sum_things();

set search_path=b,a;
select sum_things();