among patients who were prescribed with calcium acetate, what are the three most frequently prescribed drugs at the same time, until 2 years ago?
select t3.drug from ( select t2.drug, dense_rank() over ( order by count(*) desc ) as c1 from ( select admissions.subject_id, prescriptions.startdate from prescriptions join admissions on prescriptions.hadm_id = admissions.hadm_id where prescriptions.drug = 'calcium acetate' and datetime(prescriptions.startdate) <= datetime(current_time,'-2 year') ) as t1 join ( select admissions.subject_id, prescriptions.drug, prescriptions.startdate from prescriptions join admissions on prescriptions.hadm_id = admissions.hadm_id where datetime(prescriptions.startdate) <= datetime(current_time,'-2 year') ) as t2 on t1.subject_id = t2.subject_id where datetime(t1.startdate) = datetime(t2.startdate) group by t2.drug ) as t3 where t3.c1 <= 3