จนถึงปี 2101 ผู้ป่วยหายแล้วกี่ราย ไม่จำเป็นต้องใช้ทุกโต๊ะ
how many patients have been discharged until 2101?It is not neccessary to use all the tables.
 treatment:  treatmentid [ number]  patientunitstayid [ number]  treatmentname [ text]  treatmenttime [ time] 
SELECT COUNT(DISTINCT patient.uniquepid) FROM patient WHERE NOT patient.hospitaldischargetime IS NULL AND STRFTIME('%y', patient.hospitaldischargetime) <= '2101'