Cheatsheet Pages / SQL Cheatsheet
How to count, sum and average in SQL — COUNT / SUM / AVG
You need headcount, total payroll and average salary in a single result row.
Every example runs against the cheatsheet's sample tables — departments(id, name), employees(id, name, dept_id, salary, manager_id, hired_on) and orders(id, emp_id, amount, ordered_on) — and was executed and verified against SQLite, so you can paste it in and get the same result.
SELECT COUNT(*) AS headcount, SUM(salary) AS total_payroll, AVG(salary) AS avg_salary FROM employees;
-- 7 people / total 557000 / average 79571.43