PostgreSQL: sum Function

In this PostgreSQL post explains how to use the PostgreSQL sum function with syntax and examples.

Description

The PostgreSQL sum function returns the summed value of an expression.

Syntax

The syntax for the sum function in PostgreSQL is:

SELECT sum(aggregate_expression)
FROM tables
[WHERE conditions];

OR the syntax for the sum function when grouping the results by one or more columns is:

SELECT expression1, expression2, ... expression_n,
       SUM(aggregate_expression)
FROM tables
[WHERE conditions]
GROUP BY expression1, expression2, ... expression_n;

Parameters or Arguments

expression1, expression2, ... expression_n
aggregate_expression
tables
WHERE conditions

Applies To

The sum function can be used in the following versions of PostgreSQL:

PostgreSQL 9.4, PostgreSQL 9.3, PostgreSQL 9.2, PostgreSQL 9.1, PostgreSQL 9.0, PostgreSQL 8.4

Example - With Single Expression

Let's look at some PostgreSQL sum function examples and explore how to use the sum function in PostgreSQL.

For example, you might wish to know how the combined total quantites of all inventory whose product_type is 'Hardware'.

SELECT sum(quantity) AS "Total Quantity"
FROM inventory
WHERE product_type = 'Hardware';

In this sum function example, we've aliased the sum(quantity) expression as "Total Quantity". As a result, "Total Quantity" will display as the field name when the result set is returned.

Example - Using DISTINCT

You can use the DISTINCT clause within the sum function. For example, the SQL statement below returns the combined total salary of unique salary values where the salary is above $65,000 / year.

SELECT sum(DISTINCT salary) AS "Total Salary"
FROM employees
WHERE salary > 65000;

If there were two salaries of $82,000/year, only one of these values would be used in the sum function.

Example - Using Formula

The expression contained within the sum function does not need to be a single field. You could also use a formula. For example, you might want to calculate the total commission.

SELECT sum(sales * 0.05) AS "Total Commission"
FROM orders;

Example - Using GROUP BY

In some cases, you will be required to use the GROUP BY clause with the sum function.

For example, you could also use the sum function to return the name of the department and the total quantity (in the associated department).

SELECT department, sum(quantity) AS "Total Quantity"
FROM inventory
GROUP BY department;

Because you have listed one column in your SELECT statement that is not encapsulated in the sum function, you must use a GROUP BY clause. The department field must, therefore, be listed in the GROUP BY section.

Postgresql Sum Function