SQL Sum

SQL SUM Function

The SUM() function returns the total of a numeric column. It is commonly used to calculate totals such as revenue, quantities, or balances.

Basic Syntax

SELECT SUM(column_name)
FROM table_name;

Example: Total Revenue

SELECT SUM(price) AS total_revenue
FROM orders;

Using SUM with WHERE

You can filter rows before calculating the total.

SELECT SUM(price) AS electronics_revenue
FROM products
WHERE category = 'Electronics';

Using SUM with GROUP BY

To calculate totals per category, country, or group, combine SUM with GROUP BY.

SELECT category,
       SUM(price) AS total_sales
FROM products
GROUP BY category
ORDER BY total_sales DESC;

Using SUM with Expressions

You can calculate totals from computed values, such as price multiplied by quantity.

SELECT SUM(price * quantity) AS total_revenue
FROM order_items;

NULL Behavior

SUM() ignores NULL values. If all values are NULL, the result will be NULL.

Common Mistakes

• Using SUM on non-numeric columns
• Forgetting GROUP BY when selecting additional columns
• Not handling NULL values when needed

Performance Note

Indexes can improve performance when SUM is combined with WHERE filters. However, aggregations on very large tables may still require scanning many rows.

Next Step

Continue with SQL AVG to calculate average values.