what is the count of times that patient 77987 had received a specific gravity lab test in 09/last year.
select count(*) from labevents where labevents.itemid in ( select d_labitems.itemid from d_labitems where d_labitems.label = 'specific gravity' ) and labevents.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 77987 ) and datetime(labevents.charttime,'start of year') = datetime(current_time,'start of year','-1 year') and strftime('%m',labevents.charttime) = '09'