create table if not exists migrations (
  key text CONSTRAINT pkey PRIMARY KEY
);

create or replace function idempotent(migration_name text,code text) returns void as $$
begin
if exists (select key from migrations where key=migration_name) then
  raise notice 'Migration already applied: %', migration_name;
else
  raise notice 'Running migration: %', migration_name;
  execute code;
  insert into migrations (key) VALUES (migration_name);
end if;
end;
$$ language plpgsql strict;

/* USAGE: V0001__orders.sql

do $do$ begin perform idempotent('V0001__orders', $$

CREATE TABLE orders
(
  id bigint NOT NULL,
  user_id bigint,
  address_id bigint,
  product_id bigint)

$$); end $do$;
*/