SUM

Calculates the sum of an expression.

Syntax

SUM ([DISTINCT] <expr>)

Parameter	Description
`<expr>`	The expression used to calculate the sum. Valid values for `<expr>` include column names or expressions that evaluate to numeric values.
`DISTINCT`	When specified, removes duplicate values from `<expr>` before calculating the sum.

Example

Consider a table test_scores with the following columns.

+———–+——-+ | firstname | score | +———–+——-+ | Deborah | 90 | | Albert | 50 | | Carol | 11 | | Frank | 87 | | Thomas | 85 | | Peter | 50 | | Sammy | 90 | | Humphrey | 56 | +———–+——-+

SELECT
	SUM(score)
FROM
	test_scores

Returns: 519

SELECT
	SUM (DISTINCT score)
FROM
	test_scores

One each of the duplicated 90 and 50 scores are removed from the calculation.

Returns: 379