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LEFT JOIN: Keep Everyone

MediumFreeQuerying BasicsJoinsAggregation & Grouping

A regular JOIN drops customers with no orders. A LEFT JOIN keeps them. Show every customer with their name, membership, order_count (0 if no orders), and total_spent (rounded to 2 decimals; 0 if no orders). Sort by total_spent descending, then name. This is your first encounter with how JOINs handle missing data.

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Schema

customers

customer_id	name	email	signup_date	membership	total_orders
1	John Smith	john.smith@email.com	2023-01-15	Gold	15
2	Emma Wilson	emma.wilson@email.com	2023-03-20	Silver	8
3	Michael Brown	michael.brown@email.com	2023-02-10	Gold	12

orders

order_id	customer_id	product	category	quantity	price	total	order_date	country	status
1	1	Laptop Pro	Electronics	1	1299.99	1299.99	2024-01-15	USA	completed
2	2	Wireless Mouse	Electronics	2	49.99	99.98	2024-01-16	Canada	completed
3	3	Office Chair	Furniture	1	349.99	349.99	2024-01-17	USA	completed

Expected output: Appears with order_count: 0, total_spent: 0

Hint

FROM customers c LEFT JOIN orders o ON c.customer_id = o.customer_id keeps all customers. COUNT(o.order_id) returns 0 (not NULL) for unmatched rows. For the money column: COALESCE(ROUND(SUM(o.total), 2), 0) — round first, then default the no-order customers to 0.

Concepts

SELECT LEFT JOIN GROUP BY

Practise the topic: SQL practice questions · JOIN practice · GROUP BY exercises

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LEFT JOIN: Keep Everyone

Schema

Hint

Concepts

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