The aggregate function AVG() returns the average of a given expression, usually numeric values in a column. Assume we have a table containing the yearly calculation of population in cities across the world. The records for New York City look similar to the ones below:
|New York City||8,550,405||2015|
|New York City||...||...|
|New York City||8,000,906||2005|
To select the average population of the New York City, USA from a table containing city names, population measurements, and measurement years for last ten years:
select city_name, AVG(population) avg_population from city_population where city_name = 'NEW YORK CITY';
Notice how measurement year is absent from the query since population is being averaged over time.
|New York City||8,250,754|
Note: The AVG() function will convert values to numeric types. This is especially important to keep in mind when working with dates.