Structured Query Language (SQL) · Class 12 · CBSE · Science Computer Science
A database has CUSTOMER(CustID, Name) and ORDERINFO(OrderID, CustID, Amount). Which query displays the names of customers who have not placed any ord…
Practice question from Structured Query Language (SQL) (Class 12 · CBSE · Science Computer Science), with the correct answer and a step-by-step solution.
hard · MCQ · Q-7E53BD
A database has CUSTOMER(CustID, Name) and ORDERINFO(OrderID, CustID, Amount). Which query displays the names of customers who have not placed any order?
- A.SELECT c.Name FROM CUSTOMER c LEFT JOIN ORDERINFO o ON c.CustID = o.CustID WHERE o.OrderID IS NULL;Correct answer
- B.SELECT c.Name FROM CUSTOMER c INNER JOIN ORDERINFO o ON c.CustID = o.CustID WHERE o.OrderID IS NULL;
- C.SELECT c.Name FROM CUSTOMER c RIGHT JOIN ORDERINFO o ON c.CustID = o.CustID WHERE c.CustID IS NULL;
- D.SELECT c.Name FROM CUSTOMER c LEFT JOIN ORDERINFO o ON c.CustID = o.CustID WHERE o.OrderID IS NOT NULL;
Solution
A LEFT JOIN retains every customer, including those without a matching order. For such customers, the columns from ORDERINFO contain NULL, so WHERE o.OrderID IS NULL selects exactly those customers.
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