In a B+ tree index, where are the pointers to actual data records (or the records themselves) stored?
Correct answer C. Only in the leaf nodes, which are linked together
Subject / 421 questions
Programming MCQs
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Table A(x) has rows 1, 2, 3. Table B(y) has rows 2 and NULL. SELECT COUNT(*) FROM A WHERE x NOT IN (SELECT y FROM B); What is the result?
Correct answer B. 0
Table A(x) has rows 1, 2, 2, 3. Table B(x) has rows 2, 3, 4. SELECT COUNT(*) FROM (SELECT x FROM A UNION SELECT x FROM B) t; What is returned?
Correct answer A. 4
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Table Dept(id, name) has rows (10,’HR’), (20,’IT’), (30,’Ops’). Table Emp(id, name, dept_id) has rows (1,’Ali’,10), (2,’Sara’,20), (3,’Omar’,20), (4,’Zara’,NULL). SELECT COUNT(*) FROM Emp e INNER JOIN Dept d ON e.dept_id = d.id; What is the result?
Correct answer D. 3
Table Dept(id, name) has rows (10,’HR’), (20,’IT’), (30,’Ops’). Table Emp(id, name, dept_id) has rows (1,’Ali’,10), (2,’Sara’,20), (3,’Omar’,20), (4,’Zara’,NULL). SELECT d.name, COUNT(e.id) FROM Dept d LEFT JOIN Emp e ON e.dept_id = d.id GROUP BY d.name ORDER BY d.name; Which result is produced?
Correct answer C. (HR, 1), (IT, 2), (Ops, 0)
Table Dept(id, name) has rows (10,’HR’), (20,’IT’), (30,’Ops’). Table Emp(id, name, dept_id) has rows (1,’Ali’,10), (2,’Sara’,20), (3,’Omar’,20), (4,’Zara’,NULL). SELECT d.name, COUNT(*) FROM Dept d LEFT JOIN Emp e ON e.dept_id = d.id GROUP BY d.name; What count is shown for the Ops department?
Correct answer A. 1
Table Emp(id, name, mgr_id) has rows (1,’Ayesha’,NULL), (2,’Bilal’,1), (3,’Hina’,1), (4,’Kamran’,2). SELECT e.name FROM Emp e JOIN Emp m ON e.mgr_id = m.id WHERE m.name = ‘Ayesha’ ORDER BY e.name; What is returned?
Correct answer B. Bilal, Hina
Table Emp(id, dept, salary) has rows (1,’HR’,3000), (2,’HR’,5000), (3,’IT’,4000), (4,’IT’,6000), (5,’IT’,8000). SELECT id FROM Emp e WHERE salary > (SELECT AVG(salary) FROM Emp WHERE dept = e.dept) ORDER BY id; Which ids are returned?
Correct answer C. 2, 5
Table Customer(id) has rows 1, 2, 3. Table Orders(cust_id) has rows 1, 1, 3. SELECT COUNT(*) FROM Customer c WHERE NOT EXISTS (SELECT 1 FROM Orders o WHERE o.cust_id = c.id); What is the result?
Correct answer C. 1
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Table Emp(id, salary) has rows (1,3000), (2,5000), (3,5000), (4,4000). SELECT MAX(salary) FROM Emp WHERE salary < (SELECT MAX(salary) FROM Emp); What value is returned?
Correct answer A. 4000
Table Result(name, marks) has rows (‘Ali’,80), (‘Bina’,90), (‘Chand’,80), (‘Dua’,70). SELECT name FROM Result ORDER BY marks DESC, name ASC LIMIT 2; What is returned?
Correct answer A. Bina, Ali
Table Emp(id, bonus) has rows (1,500), (2,NULL), (3,NULL), (4,200). SELECT COUNT(*) FROM Emp WHERE bonus = NULL; What is the result?
Correct answer B. 0
Table Pay(id, salary, bonus) has one row (1, 5000, NULL). SELECT salary + bonus FROM Pay; What is returned?
Correct answer A. NULL
Table Sales(region, amount) has rows (‘N’,100), (‘N’,200), (‘S’,50), (‘S’,400), (‘E’,300). SELECT COUNT(*) FROM (SELECT region FROM Sales WHERE amount >= 100 GROUP BY region HAVING COUNT(*) >= 2) t; What is the result?
Correct answer A. 1
Table T(dept) has rows ‘HR’, NULL, ‘IT’, NULL, ‘HR’. SELECT dept, COUNT(*) FROM T GROUP BY dept; How many rows does this query return?
Correct answer C. 3
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Table Emp(id, salary) has rows (1,3000), (2,5000), (3,4000). CREATE VIEW HighPaid AS SELECT * FROM Emp WHERE salary > 4000; UPDATE Emp SET salary = 4500 WHERE id = 1; SELECT COUNT(*) FROM HighPaid; What does the final SELECT return?
Correct answer C. 2
Table Acc(id) has 2 rows. The following runs: BEGIN; INSERT INTO Acc VALUES (3); SAVEPOINT s1; INSERT INTO Acc VALUES (4); ROLLBACK TO SAVEPOINT s1; COMMIT; How many rows does Acc now contain?
Correct answer D. 3
Table Stock(item, qty) has rows (‘a’,8), (‘b’,12), (‘c’,20), (‘d’,15). UPDATE Stock SET qty = qty – 5 WHERE qty > 10; SELECT SUM(qty) FROM Stock; What is the result?
Correct answer D. 40
Table Exam(roll, marks) has marks 45, 50, 72, 38 and 90. SELECT SUM(CASE WHEN marks >= 50 THEN 1 ELSE 0 END) FROM Exam; What is returned?
Correct answer D. 3
Table Colour(c) has rows ‘red’, ‘blue’. Table Size(s) has rows ‘S’, ‘M’, ‘L’. SELECT COUNT(*) FROM Colour CROSS JOIN Size; What is the result?
Correct answer C. 6