Most asked MySQL MCQs focused on Table and Join Operations Output for UGC NET, SET, EMRS, KVS, ISRO, and Assistant Professor exams.
21. Given the following tables, what will be the output of an INNER JOIN?
Customers Table
| CustomerID | Name | City |
|---|---|---|
| 1 | Alice | Delhi |
| 2 | Bob | Mumbai |
| 3 | Charlie | Kolkata |
Orders Table
| OrderID | CustomerID | Product |
|---|---|---|
| 101 | 1 | Laptop |
| 102 | 2 | Mobile |
| 103 | 4 | Tablet |
Query:
SELECT Customers.Name, Orders.Product
FROM Customers
INNER JOIN Orders ON Customers.CustomerID = Orders.CustomerID;
A) Returns all customers with their respective orders
B) Returns customers who have placed orders
C) Returns all customers, even if they don’t have an order
D) Returns all orders, even if they don’t have a customer
Answer: B) Returns customers who have placed orders
(Output: Alice - Laptop, Bob - Mobile)
22. What will a LEFT JOIN return when there is no matching row in the right table?
A) NULL values for the right table columns
B) Exclude those rows
C) Return only matching rows
D) Throw an error
Answer: A) NULL values for the right table columns
23. What does the following query return?
SELECT C.Name, O.Product
FROM Customers C
LEFT JOIN Orders O ON C.CustomerID = O.CustomerID;
A) Only customers who placed an order
B) All customers, with NULL for those who haven't placed an order
C) All orders, even if they don’t have a customer
D) Only orders with matching customers
Answer: B) All customers, with NULL for those who haven't placed an order
24. Which JOIN returns only unmatched rows from both tables?
A) INNER JOIN
B) LEFT JOIN
C) RIGHT JOIN
D) FULL OUTER JOIN
Answer: D) FULL OUTER JOIN
25. Given two tables, what will be the output of a CROSS JOIN?
Employees Table
| EmpID | Name |
|---|---|
| 1 | Raj |
| 2 | Anil |
Departments Table
| DeptID | DeptName |
|---|---|
| 101 | HR |
| 102 | IT |
Query:
SELECT Employees.Name, Departments.DeptName
FROM Employees
CROSS JOIN Departments;
A) 2 rows
B) 4 rows
C) 1 row
D) No rows
Answer: B) 4 rows (Each employee gets paired with every department)
26. Which SQL clause is used to filter grouped records?
A) WHERE
B) GROUP BY
C) HAVING
D) ORDER BY
Answer: C) HAVING
27. What will be the result of the following query?
SELECT Customers.Name, Orders.Product
FROM Customers
RIGHT JOIN Orders ON Customers.CustomerID = Orders.CustomerID;
A) Only customers who placed an order
B) All customers, even if they haven't placed an order
C) All orders, even if they don’t have a customer
D) Only unmatched customers
Answer: C) All orders, even if they don’t have a customer
28. If there are 5 rows in Table A and 3 rows in Table B, how many rows will a CROSS JOIN return?
A) 5
B) 3
C) 8
D) 15
Answer: D) 15 (5 × 3)
29. What will be the output of the following query?
SELECT Customers.Name, Orders.Product
FROM Customers
FULL JOIN Orders ON Customers.CustomerID = Orders.CustomerID;
A) MySQL does not support FULL JOIN
B) Returns only matching records
C) Returns only unmatched records
D) Returns an error
Answer: A) MySQL does not support FULL JOIN (It requires UNION of LEFT JOIN and RIGHT JOIN)
30. Which SQL JOIN returns all records from the left table and matching records from the right table?
A) INNER JOIN
B) LEFT JOIN
C) RIGHT JOIN
D) FULL OUTER JOIN
Answer: B) LEFT JOIN
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