Ordering
Eliminating duplicate results
Aggregation
12. Count distinctive values in a column
Grouping
HAVING: filtering and ordering groups
Let's practice

Instruction

Great. As you probably expect, we can also add the keyword DISTINCT in our function count():

SELECT
  count(DISTINCT customer_id) 
FROM orders;

This time, we count all rows which have a distinctive value in the column customer_id. In other words, this instruction tells us how many different customers have placed an order so far. If a customer places 5 orders, the customer will only be counted once.

Exercise

Count how many different positions there are in the table employees.

Stuck? Here's a hint!

Type:

SELECT 
  count(DISTINCT position) 
FROM employees;