Given a table orders with columns order_id, customer_id, and status, write a query to find the number of customers who have placed at least one order with status 'completed'.
hard📝 Application Q9 of 15
SQL - Aggregate Functions
Given a table orders with columns order_id, customer_id, and status, write a query to find the number of customers who have placed at least one order with status 'completed'.
ASELECT COUNT(customer_id) FROM orders WHERE status = 'completed';
BSELECT COUNT(*) FROM orders WHERE status = 'completed';
CSELECT COUNT(DISTINCT customer_id) FROM orders WHERE status = 'completed';
DSELECT COUNT(DISTINCT order_id) FROM orders WHERE status = 'completed';
Step-by-Step Solution
Solution:
Step 1: Filter orders with status 'completed'
Use WHERE status = 'completed' to select only completed orders.
Step 2: Count distinct customers who placed these orders
Use COUNT(DISTINCT customer_id) to count unique customers.
Final Answer:
SELECT COUNT(DISTINCT customer_id) FROM orders WHERE status = 'completed'; -> Option C
