SQL Left Join Basics | Dataford Interview Questions

What is a left join in SQL?

Write a PostgreSQL query that demonstrates the behavior of a left join by combining customers with their orders. The result must retain customers that do not have a matching order and show NULL order fields for them.

Output

One row per customer-order relationship, including customers without orders
Columns: customer_id, customer_name, order_id, order_amount
Sort by customer_id ascending, then order_id ascending, with unmatched customers included

Schema

customers

Column	Type	Description
customer_idPK	INT	Unique customer identifier
customer_name	VARCHAR(100)	Customer name

orders

Column	Type	Description
order_idPK	INT	Unique order identifier
customer_id	INT	Customer associated with the order
order_amount	DECIMAL(10,2)	Order amount

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Problem