count the number of people who were prescribed lr within 2 months following a diagnosis of personal history of fall since 4 years ago.
select count( distinct t1.subject_id ) from ( select admissions.subject_id, diagnoses_icd.charttime from diagnoses_icd join admissions on diagnoses_icd.hadm_id = admissions.hadm_id where diagnoses_icd.icd9_code = ( select d_icd_diagnoses.icd9_code from d_icd_diagnoses where d_icd_diagnoses.short_title = 'personal history of fall' ) and datetime(diagnoses_icd.charttime) >= datetime(current_time,'-4 year') ) as t1 join ( select admissions.subject_id, prescriptions.startdate from prescriptions join admissions on prescriptions.hadm_id = admissions.hadm_id where prescriptions.drug = 'lr' and datetime(prescriptions.startdate) >= datetime(current_time,'-4 year') ) as t2 on t1.subject_id = t2.subject_id where t1.charttime < t2.startdate and datetime(t2.startdate) between datetime(t1.charttime) and datetime(t1.charttime,'+2 month')