SELECT sysdate - 1 FROM dual; -- Yesterday 12/01/2021 14:27:27
SELECT trunc(sysdate) - 1 FROM dual; -- Yesterday 12/01/2021 00:00:00
SELECT sysdate - 1 / 24 FROM dual; -- 1 hour ago
SELECT sysdate - 1 / 24 / 60 FROM dual; -- 1 minute ago
SELECT add_months(trunc(sysdate), -1) FROM dual; -- 1 month ago (no time)
SELECT trunc(sysdate) - 30 FROM dual; -- 30 days ago (no time)
SELECT add_months(trunc(sysdate), -12*2) FROM dual; -- 2 years ago (no time)