Adds up values from many rows and returns the total.
SUM(<expression>)
SUM(DISTINCT <expression>)
An aggregate function: it turns a group of rows into one number — the total. It skips NULL. Together with GROUP BY it calculates the total separately for each group: revenue by month, salaries by department.
employees
| name | department | salary | bonus | phone |
|---|---|---|---|---|
| Emma | backend | 1200 | 300 | +44 7700 900123 |
| Liam | backend | 1000 | NULL | NULL |
| Olivia | frontend | 1350 | 150 | +44 7700 900456 |
| Noah | frontend | 950 | NULL | +44 7700 900789 |
| Sophia | design | 1200 | 200 | NULL |
orders
| id | created_at | amount |
|---|---|---|
| 1 | 2026-07-03 10:15:00 | 120.50 |
| 2 | 2026-07-28 18:40:00 | 80.25 |
| 3 | 2026-08-09 09:05:00 | 199.99 |
| 4 | 2026-08-21 14:30:00 | 45.00 |
| 5 | 2026-09-02 11:00:00 | 64.75 |
These tables already exist in the sandbox — the examples below use them. Want to try this in your own database? Copy the SQL.
| revenue |
|---|
| 510.49 |
| department | payroll |
|---|---|
| backend | 2200 |
| design | 1200 |
| frontend | 2300 |
| total_bonus | salary_plus_bonus | sum_of_sums |
|---|---|---|
| 650 | 4400 | 6350 |
salary + bonus gives NULL for Liam and Noah, so their salaries dropped out of the second total entirely: 4400 instead of 6350.
If there are no rows or all the values are NULL, the result is NULL, not 0. If you need a zero — COALESCE(SUM(amount), 0).
A NULL inside an expression “swallows” the whole row: SUM(salary + bonus) won't count the salary of those with no bonus. Write SUM(salary + COALESCE(bonus, 0)).