How to Find the Average of a Numeric Column in SQL

Database:

Operators:

AVG

Problem:

You’d like to calculate the average of numbers stored in a column.

Example:

Our database has a table named sale with data in the following columns: id, city, year, and amount.

id	city	year	amount
1	Los Angeles	2017	2345.50
2	Chicago	2018	1345.46
3	Annandale	2016	900.56
4	Annandale	2017	23230.22
5	Los Angeles	2018	12456.20
6	Chicago	2017	89000.40
7	Annandale	2018	21005.77
8	Chicago	2016	2300.89

Let’s calculate the average sales, regardless of city or year.

Solution:

SELECT AVG(amount) as avg_amount
FROM sale;

Here’s the result:

avg_amount
19073.125000

Discussion:

If you’d like to calculate the average of numeric values stored in a column, you can do so using the AVG() aggregate function; it takes as its argument the name of the column whose average you want to calculate. If you haven’t specified any other columns in the SELECT clause, the average will be calculated for all records in the table.

Of course, since it’s an aggregate function, AVG() can also be used with groups. For example, if we’d like to find the average sale per city, we can write this query:

SELECT city, AVG(amount) as avg_amount
FROM sale
GROUP BY city;

The average is calculated for each city:

city	amount
Los Angeles	7400.850000
Chicago	30882.250000
Annandale	15045.516667

Additionally, if the average has to be rounded, you can pass the result of the AVG() function into ROUND():

SELECT city, 
  ROUND(AVG(amount), 2) as avg_amount
FROM sale
GROUP BY city;