drop   table if exists testtable;
create table           testtable (pk int primary key, foo text, bar text);
create unique index foobar_idx on testtable (pk, foo, bar);
INSERT INTO testtable (pk, foo, bar) VALUES (1, 'Hello', 'World') ON CONFLICT (pk,foo,bar) DO NOTHING;
INSERT INTO testtable (pk, foo, bar) VALUES (1, 'Hello', 'World') ON CONFLICT (pk,foo,bar) DO NOTHING;
INSERT INTO testtable (pk, foo, bar) VALUES (1, 'Hello', 'Quz'  ) ON CONFLICT (pk,foo,bar) DO NOTHING;