How much is the average salary of female employees in comparison to male employees?
female refers to Gender = 'F'; male refers to Gender = 'M'; difference in the average salary of female against male employees = SUBTRACT(AVG(Rate where Gender = 'F')), (AVG(Rate where Gender = 'M')));
SELECT AVG(T2.Rate) FROM Employee AS T1 INNER JOIN EmployeePayHistory AS T2 ON T1.BusinessEntityID = T2.BusinessEntityID WHERE T1.Gender = 'F'