ในปีนี้มีผู้ป่วยกี่รายที่ได้รับวิตามินเอ?ไม่จำเป็นต้องใช้ทุกตาราง
in this year, how many patients were prescribed vitamin a?It is not neccessary to use all the tables.
 labevents:  row_id [ number]  subject_id [ number]  hadm_id [ number]  itemid [ number]  charttime [ time]  valuenum [ number]  valueuom [ text] 
SELECT COUNT(DISTINCT admissions.subject_id) FROM admissions WHERE admissions.hadm_id IN (SELECT prescriptions.hadm_id FROM prescriptions WHERE prescriptions.drug = 'vitamin a' AND DATETIME(prescriptions.startdate, 'start of year') = DATETIME(CURRENT_TIME(), 'start of year', '-0 year'))