how much of patient 94956's glucose second measured on the first hospital visit changed compared to the first value measured on the first hospital visit?
select ( select labevents.valuenum from labevents where labevents.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 94956 and admissions.dischtime is not null order by admissions.admittime asc limit 1 ) and labevents.itemid in ( select d_labitems.itemid from d_labitems where d_labitems.label = 'glucose' ) order by labevents.charttime asc limit 1 offset 1 ) - ( select labevents.valuenum from labevents where labevents.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 94956 and admissions.dischtime is not null order by admissions.admittime asc limit 1 ) and labevents.itemid in ( select d_labitems.itemid from d_labitems where d_labitems.label = 'glucose' ) order by labevents.charttime asc limit 1 )