count the number of patients who received a incise cerebral meninges procedure during the same month after they had received a serum transfusion nec procedure during this year.
select count( distinct t1.subject_id ) from ( select admissions.subject_id, procedures_icd.charttime from procedures_icd join admissions on procedures_icd.hadm_id = admissions.hadm_id where procedures_icd.icd9_code = ( select d_icd_procedures.icd9_code from d_icd_procedures where d_icd_procedures.short_title = 'serum transfusion nec' ) and datetime(procedures_icd.charttime,'start of year') = datetime(current_time,'start of year','-0 year') ) as t1 join ( select admissions.subject_id, procedures_icd.charttime from procedures_icd join admissions on procedures_icd.hadm_id = admissions.hadm_id where procedures_icd.icd9_code = ( select d_icd_procedures.icd9_code from d_icd_procedures where d_icd_procedures.short_title = 'incise cerebral meninges' ) and datetime(procedures_icd.charttime,'start of year') = datetime(current_time,'start of year','-0 year') ) as t2 on t1.subject_id = t2.subject_id where t1.charttime < t2.charttime and datetime(t1.charttime,'start of month') = datetime(t2.charttime,'start of month')