what is the maximum hospital cost that involves a procedure, called closed bx skin/subq tiss during the previous year?
select max(t1.c1) from ( select sum(cost.cost) as c1 from cost where cost.hadm_id in ( select procedures_icd.hadm_id from procedures_icd where procedures_icd.icd9_code = ( select d_icd_procedures.icd9_code from d_icd_procedures where d_icd_procedures.short_title = 'closed bx skin/subq tiss' ) ) and datetime(cost.chargetime,'start of year') = datetime(current_time,'start of year','-1 year') group by cost.hadm_id ) as t1