sum
Calculates the sum. Only works for numbers.
Syntax
sum(num)
Parameters
Returned value
Example
First we create a table employees and insert some fictional employee data into it.
Query:
CREATE TABLE employees
(
    `id` UInt32,
    `name` String,
    `salary` UInt32
)
ENGINE = Log
INSERT INTO employees VALUES
    (87432, 'John Smith', 45680),
    (59018, 'Jane Smith', 72350),
    (20376, 'Ivan Ivanovich', 58900),
    (71245, 'Anastasia Ivanovna', 89210);
We query for the total amount of the employee salaries using the sum function. 
Query:
SELECT sum(salary) FROM employees;
Result:
   ┌─sum(salary)─┐
1. │      266140 │
   └─────────────┘