SQL practice: GROUP BY: One Answer Per Group

Count the orders per status.

Count the customers per customer_type.

Find the average salary per role, and show the headcount beside it.

Count the branches per region.

Find the total quantity sold per product_id.

Count how many products fall under each thickness_mm value. What happens to the accessories?

Count the orders per branch, counting only Delivered ones.

For each customer_type, show how many customers there are and the earliest signup_date.

For each branch, show total orders, delivered orders and cancelled orders as three separate columns.

Count how many employees report to each manager_id.

Find the total revenue per product_id from order_items (quantity × unit_price).

Why does SELECT branch_id, order_date, COUNT(*) FROM orders GROUP BY branch_id; fail? Fix it by aggregating order_date with MAX() as latest_order so each branch has one summary row.

Fix this query so it correctly counts the number of products in each category.