aggregate

SUM()

Adds up all the values in a numeric column across a group of rows.

Description

SUM is an aggregate function that adds together all the values in a numeric column across the rows in a result set. It's one of the most common functions for reporting totals, like total revenue, total quantity sold, or total salary paid.

Syntax

SUM(column_name)

Parameters

Name	Description	Optional
expression	The numeric column or expression whose values should be added together. NULL values are ignored.	No

Return Type

SUM typically returns a DOUBLE (or a larger integer type when summing integers), matching or widening the type of the input column so the total doesn't overflow.

Examples

Store (Customers/Orders/Products)

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Store (Customers/Orders/Products)

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NULLs don't break your total

SUM ignores NULL values rather than turning the whole result into NULL. If every value in the group is NULL, SUM returns NULL, but a mix of numbers and NULLs still sums correctly.

Common Mistakes

Summing a column that isn't actually numeric, like an ID column, which produces a meaningless total.
Forgetting GROUP BY. SELECT customer_id, SUM(quantity) FROM orders without GROUP BY customer_id will error in most databases because customer_id isn't aggregated.
Confusing SUM with COUNT. SUM(quantity) adds up the quantities themselves, while COUNT(quantity) just counts how many rows have a quantity value, regardless of its size.