psql -v ON_ERROR_STOP=1 -c begin $(find . -name '*.sql' -printf ' -f %f\n' | sort -V | xargs) -c commit

0_setup.sql

create table if not exists migration (
    id bigint primary key,
    at timestamptz not null default clock_timestamp()
);

1_test.sql

select not exists(select true from migration where id = 1) as should_v1 \gset
\if :should_v1
create table test (id int);
insert into migration (id) values (1);
\endif

2_test.sql

select not exists(select true from migration where id = 2) as should_v2 \gset
\if :should_v2
alter table test add col2 text;
insert into migration (id) values (2);
\endif