What is the pay frequency of the oldest employee?
oldest employee refers to min(BirthDate); PayFrequency = 1 refers to ‘Salary received monthly’; PayFrequency = 2 refers to ‘Salary received biweekly'
SELECT T1.PayFrequency FROM EmployeePayHistory AS T1 INNER JOIN Employee AS T2 ON T1.BusinessEntityID = T2.BusinessEntityID ORDER BY T2.BirthDate ASC LIMIT 1