This column function returns the average of a set of numbers. The argument values must be numbers.
Example:
Using the PROJECT table, return the average staffing level (PRSTAFF) of projects in department (DEPTNO) 'D11'.
SELECT AVG(PRSTAFF) FROM PROJECT WHERE DEPTNO = 'D11'
Returns 4.25 (that is, 17/4) when using the sample table.