sum

CREATE TABLE employees
(
    id UInt32,
    name String,
    salary UInt32
)
ENGINE = Memory;

INSERT INTO employees VALUES
    (87432, 'John Smith', 45680),
    (59018, 'Jane Smith', 72350),
    (20376, 'Ivan Ivanovich', 58900),
    (71245, 'Anastasia Ivanovna', 89210);

SELECT sum(salary) FROM employees;

┌─sum(salary)─┐
│      266140 │
└─────────────┘

CREATE TABLE requests
(
    req_id UInt32,
    duration IntervalMillisecond
)
ENGINE = Memory;

INSERT INTO requests VALUES (1, 100), (2, 200), (3, 300);

SELECT sum(duration) AS total_duration, toTypeName(total_duration) FROM requests;

┌─total_duration─┬─toTypeName(total_duration)─┐
│            600 │ IntervalMillisecond        │
└────────────────┴────────────────────────────┘