SQL Server: AVG Function
This SQL Server tutorial explains how to use the AVG function in SQL Server (Transact-SQL) with syntax and examples.
In SQL Server (Transact-SQL), the AVG function returns the average value of an expression.
The syntax for the AVG function in SQL Server (Transact-SQL) is:
SELECT AVG(aggregate_expression) FROM tables [WHERE conditions];
OR the syntax for the AVG function when grouping the results by one or more columns is:
SELECT expression1, expression2, ... expression_n, AVG(aggregate_expression) FROM tables [WHERE conditions] GROUP BY expression1, expression2, ... expression_n;
Parameters or Arguments
- expression1, expression2, … expression_n
- Expressions that are not encapsulated within the AVG function and must be included in the GROUP BY clause at the end of the SQL statement.
- This is the column or expression that will be averaged.
- The tables that you wish to retrieve records from. There must be at least one table listed in the FROM clause.
- WHERE conditions
- Optional. These are conditions that must be met for the records to be selected.
The AVG function can be used in the following versions of SQL Server (Transact-SQL):
- SQL Server 2017, SQL Server 2016, SQL Server 2014, SQL Server 2012, SQL Server 2008 R2, SQL Server 2008, SQL Server 2005
Example – With Single Field
Let’s look at some SQL Server AVG function examples and explore how to use the AVG function in SQL Server (Transact-SQL).
For example, you might wish to know how the average quantity of all products where the quantity is greater than 0.
SELECT AVG(quantity) AS "Average Quantity" FROM products WHERE quantity > 0;
In this AVG function example, we’ve aliased the AVG(quantity) expression as “Average Quantity”. As a result, “Average Quantity” will display as the field name when the result set is returned.
Example – Using DISTINCT
You can use the DISTINCT clause within the AVG function. For example, the SQL statement below returns the average salary of unique salary values where the salary is above $40,000 / year.
SELECT AVG(DISTINCT salary) AS "Average Salary" FROM employees WHERE salary > 40000;
If there were two salaries of $50,000/year, only one of these values would be used in the AVG function.
Example – Using Formula
The expression contained within the AVG function does not need to be a single field. You could also use a formula. For example, you might want the average commission.
SELECT AVG(order_value * 0.10) AS "Average Commission" FROM order_details;
Example – Using GROUP BY
You could also use the AVG function to return the name of the department and the average quantity (in the associated department). For example,
SELECT department, AVG(quantity) AS "Average Quantity" FROM products GROUP BY department;
Because you have listed one column in your SELECT statement that is not encapsulated in the AVG function, you must use a GROUP BY clause. The department field must, therefore, be listed in the GROUP BY section.