ปัจจุบันมีผู้ป่วยอายุ 50 ปีขึ้นไปกี่คน?ไม่จำเป็นต้องใช้ตารางทั้งหมด
how many current patients are of age 50s?It is not neccessary to use all the tables.
 vitalperiodic:  vitalperiodicid [ number]  patientunitstayid [ number]  temperature [ number]  sao2 [ number]  heartrate [ number]  respiration [ number]  systemicsystolic [ number]  systemicdiastolic [ number]  systemicmean [ number]  observationtime [ time] 
SELECT COUNT(DISTINCT patient.uniquepid) FROM patient WHERE patient.hospitaldischargetime IS NULL AND patient.age BETWEEN 50 AND 59