A data engineer needs to find all customers who have never placed an order.

A left anti-join returns rows from the left-side relation for which no matching row exists in the right-side relation. By placing customers on the left and orders on the right and joining by customer_id, the result contains precisely the customers who have no corresponding order. A left anti-join also returns only columns from the left relation, which satisfies the requirement to exclude all order-related fields. A left outer join could produce the desired result only with an additional NULL filter and correct table order. An inner join returns customers who have placed orders, which is the opposite requirement. A full outer join can introduce order-only rows and unnecessary columns. Therefore, the left anti-join described in option C is the most exact and efficient expression for this requirement.

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