Handle Nulls in Large Joins | Dataford Interview Questions

How would you handle null values when performing a join between two large tables?

Using the supplied orders and customer_accounts tables, write a query that preserves every order, avoids matching NULL customer keys, substitutes readable values for missing account attributes, and classifies each order's match status.

Output

One row per order with order_id, customer_id, customer_name, segment, and join_status.
Include matched orders, orders with NULL customer IDs, and orders with non-matching customer IDs.
Sort by order_id ascending.

Schema

orders

Column	Type	Description
order_idPK	INT	Unique order identifier
customer_id	INT	Customer account identifier, when available
order_amount	DECIMAL(10,2)	Order value
order_channel	VARCHAR(30)	Channel through which the order was placed

customer_accounts

Column	Type	Description
customer_idPK	INT	Unique customer account identifier
customer_name	VARCHAR(100)	Customer display name
segment	VARCHAR(40)	Customer segment
account_status	VARCHAR(20)	Current account status

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Problem