AVG

AVG gives the average (the mean) of a whole column or a group of rows for a single column of values.

AVG is an aggregate function it is normally used with GROUP BY.

The mean of the values 2, 5, 5 is (2+5+5)/3 = 12/3 = 4, you divide by 3 because there are 3 numbers in this example.

NULL values do not contribute to the calculation.

    SELECT region, AVG(population)
    FROM bbc
   GROUP BY region

With a GROUP BY region statement each region shows up just once. The AVG column gives the average population per country for each region.

SELECT region, AVG(population)
  FROM bbc
 GROUP BY region