Ordering
Eliminating duplicate results
Aggregation
Grouping
18. Find the average value in groups
HAVING: filtering and ordering groups
Let's practice

## Instruction

That's right!

Let's study one more example of this kind:

SELECT
customer_id,
avg(total_sum)
FROM orders
GROUP BY customer_id;


As you can see, we now have the function avg(total_sum) which will count the average order value for each of our customers.

## Exercise

Find the average salary in each department in 2015.

### Stuck? Here's a hint!

Type:

SELECT
department,
avg(salary)
FROM employees
WHERE year = 2015
GROUP BY department;