PL SQL-,Nth highest,MAX ,2nd MAX and AVERAGE

SELECT DISTINCT(A.SALARY) FROM EMPLOYEE A
WHERE &SALARY = (SELECT COUNT(DISTINCT(B.SALARY)) FROM EMPLOYEE B
WHERE A.SALARY<=B.SALARY); 

&salary=nth number for nth highest salary.


MAX and SECOND MAX
NOTE : Select The second Highest

SELECT MAX(salary) FROM employees WHERE salary < (SELECT MAX(salary) FROM employees)

NOTE :If there are ties then get the second highest as below :

Name    Salary
Jim       6
Foo       5
Bar       5
Steve     4
SELECT name, salaryFROM employeesWHERE salary = (SELECT MAX(salary) FROM employees WHERE salary < (SELECT MAX(salary) FROM employees))

AVERAGE 

SELECT 
  DepartmentID, 
  Avg(tblEmployeeInfo.Salary) AS DeptAvgSalary
FROM tblEmployeeInfo
GROUP BY DepartmentID;