instruction: what are the four most frequent procedures performed since 3 years ago?
response: SELECT t1.treatmentname FROM (SELECT treatment.treatmentname, DENSE_RANK() OVER (ORDER BY COUNT(*) DESC) AS c1 FROM treatment WHERE DATETIME(treatment.treatmenttime) >= DATETIME(CURRENT_TIME(), '-3 year') GROUP BY treatment.treatmentname) AS t1 WHERE t1.c1 <= 4