ปีนี้ผู้ป่วยที่ออกจากโรงพยาบาลได้เป็นจำนวนเท่าใด ไม่จำเป็นต้องใช้ทุกโต๊ะ
what was the number of patients that were discharged from hospital in this year?It is not neccessary to use all the tables.
 diagnosis:  diagnosisid [ number]  patientunitstayid [ number]  diagnosisname [ text]  diagnosistime [ time]  icd9code [ text] 
SELECT COUNT(DISTINCT patient.uniquepid) FROM patient WHERE NOT patient.hospitaldischargetime IS NULL AND DATETIME(patient.hospitaldischargetime, 'start of year') = DATETIME(CURRENT_TIME(), 'start of year', '-0 year')