SQL Aggregate Functions: Mastering the SUM Function

Using SUM in Basic Queries

You can use SUM in a SELECT statement to add up values from a column.

This is helpful when you want the total of a column for the entire table or filtered rows.

• Example: SELECT SUM(sales) FROM orders;
• This returns the total sales amount from the orders table.

Combining SUM with GROUP BY

SUM is often combined with GROUP BY to calculate totals per category.

GROUP BY groups rows that share a common value, and SUM calculates the total for each group.

• Example: SELECT department, SUM(salary) FROM employees GROUP BY department;
• This query returns the total salary expense per department.

Handling NULL Values in SUM

SUM automatically ignores NULL values in the column when calculating totals.

This means NULLs do not affect the sum result.

• If all values are NULL, SUM returns NULL.
• Use COALESCE to replace NULLs if needed before summing.

Practical Examples of SUM

Let's look at some practical examples to understand how SUM works in real queries.