How to Filter Records with Aggregate Function SUM

Problem:

You need to filter groups of rows by the sum of a given column.

Example:

Our database has a table named company with data in the following columns: id, department, first_name, last_name, and salary.

Let’s find the names of departments that have sums of salaries of its employees less than 7000.

Solution:

SELECT department, SUM(salary)
FROM company
GROUP BY department
HAVING SUM(salary) < 7000;

Here’s the result:

Discussion:

In this query, you calculate the sum of salaries for employees of each department. Because you calculate the value for each group of rows (we group rows by department name), the query has a GROUP BY clause with the name of the column to group rows (GROUP BY department). To calculate the sum of values for each group of rows, we use the aggregate SUM function, and give it the column salary as an argument.

To filter records using the aggregate function, we use the HAVING clause. Remember, HAVING should be put after GROUP BY clause. HAVING contains the condition comparing the value returned by the aggregate function with a given value. Here, our condition is SUM(salary) < 7000: we verify the salary sum in each department is lower than 7000.

The query displayed only one department, finance, with salaries of 6550.