You can do this in postgres as well, with something like:

    begin; alter table t2 disable trigger all;
    insert into t2 (t1_id) values (20);
    alter table t2 enable trigger all;
    commit;

Setting constraints to deferrable/initially deferred[1] is probably a nicer way for any non-insane thing you're trying to achieve with such, though :)

[1] https://www.postgresql.org/docs/9.6/static/sql-set-constrain...