Aggregate and Analytic Functions

Aggregate Example
The following example calculates the average salary of all employees in the hr.employees table:

SELECT AVG(salary) "Average"
  FROM employees;

       Average
--------------
    6461.83178

Analytic Example

The following example calculates, for each employee in the employees table, the average salary of the employees reporting to the same manager who were hired in the range just before through just after the employee:

SELECT manager_id, last_name, hire_date, salary,
       AVG(salary) OVER (PARTITION BY manager_id ORDER BY hire_date 
  ROWS BETWEEN 1 PRECEDING AND 1 FOLLOWING) AS c_mavg
  FROM employees
  ORDER BY manager_id, hire_date, salary;

MANAGER_ID LAST_NAME                 HIRE_DATE     SALARY     C_MAVG
---------- ------------------------- --------- ---------- ----------
       100 De Haan                   13-JAN-01      17000      14000
       100 Raphaely                  07-DEC-02      11000 11966.6667
       100 Kaufling                  01-MAY-03       7900 10633.3333
       100 Hartstein                 17-FEB-04      13000 9633.33333
       100 Weiss                     18-JUL-04       8000 11666.6667
       100 Russell                   01-OCT-04      14000 11833.3333
       100 Partners                  05-JAN-05      13500 13166.6667
       100 Errazuriz                 10-MAR-05      12000 11233.3333
. . .