Database Systems Practice Test 2026 - Free Database Practice Questions and Study Guide

To get the total of a numeric column, you need an operation that adds up all the values. The sum function does exactly that by aggregating and returning the total across the selected rows. The average function would compute the mean, not the total; min returns the smallest value; and count tells you how many rows (or non-null values) exist, not the sum of their values. In most databases, NULLs are ignored by sum, so they don’t affect the total (if all values are NULL, the result is typically NULL). So the sum function is the correct choice for calculating the total.