instruction: what are the four most common lab tests among the patients aged 50s in 2101?
response: SELECT t1.labname FROM (SELECT lab.labname, DENSE_RANK() OVER (ORDER BY COUNT(*) DESC) AS c1 FROM lab WHERE lab.patientunitstayid IN (SELECT patient.patientunitstayid FROM patient WHERE patient.age BETWEEN 50 AND 59) AND STRFTIME('%y', lab.labresulttime) = '2101' GROUP BY lab.labname) AS t1 WHERE t1.c1 <= 4