Data Cleaning and Join Differences | Dataford Interview Questions

What techniques would you use for data cleaning, and how do INNER JOIN and LEFT JOIN differ?

For the SQL portion, clean the supplied customer and order records, retain customers without valid orders, and explain why the selected join preserves them.

Output

One row per customer with customer_id, customer_name, cleaned_email, valid_order_count, and valid_order_total.
Include every customer, count only positive completed or paid orders, and sort by customer_id ascending.

Schema

raw_customers

Column	Type	Description
customer_idPK	INT	Unique customer identifier
customer_name	VARCHAR(100)	Customer name, potentially containing extra whitespace
email	VARCHAR(255)	Customer email address, potentially inconsistent or blank

raw_orders

Column	Type	Description
order_idPK	INT	Unique order identifier
customer_id	INT	Customer associated with the order
amount	DECIMAL(10,2)	Order amount
status	VARCHAR(30)	Raw order status

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