Computes the average of a numeric expression for a set of rows, or computes the average of a set of unique values.
AVG ( numeric-expression | DISTINCT column-name )
numeric-expression The value whose average is calculated over a set of rows.
DISTINCT column-name Computes the average of the unique values in column-name. This is of limited usefulness, but is included for completeness.
The following statement returns the value 49988.6.
SELECT AVG ( salary ) FROM employee
This average does not include rows where numeric -expression is the NULL value. Returns the NULL value for a group containing no rows.