Ordering
Eliminating duplicate results
Aggregation
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) AS distinct_customers 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. Name the column distinct_positions.
Stuck? Here's a hint!
Type:
SELECT COUNT(DISTINCT position) AS distinct_positions FROM employees;
