Test your Database Management Systems basics: keys and constraints, SQL queries, joins, normal forms and ACID transactions. These topics appear in nearly every placement aptitude test and technical interview.
How to practise: read each question and tap the option you think is correct. You will see right away whether you got it, along with a short explanation, and your score is tracked at the bottom of the screen. This set has 16 questions.
Q1. A minimal set of attributes that uniquely identifies every row in a table is called a:
a) Super key
b) Candidate key
c) Foreign key
d) Composite attribute
Q2. A foreign key is used to:
a) Speed up every query
b) Link a table to the primary key of another table
c) Store encrypted values
d) Make a column unique
Q3. Which SQL command is a DDL command that removes all rows from a table at once while keeping the table structure?
a) DELETE
b) DROP
c) TRUNCATE
d) REMOVE
Q4. Which clause filters groups created by GROUP BY?
a) WHERE
b) HAVING
c) ORDER BY
d) LIMIT
Q5. Table Emp has 5 rows and table Dept has 4 rows. How many rows does SELECT * FROM Emp CROSS JOIN Dept return?
a) 9
b) 5
c) 4
d) 20
Q6. Which join returns all rows from the left table and only matching rows from the right table?
a) INNER JOIN
b) LEFT OUTER JOIN
c) RIGHT OUTER JOIN
d) SELF JOIN
Q7. What does SELECT COUNT(*) count compared with COUNT(column)?
a) They are always identical
b) COUNT(*) counts all rows; COUNT(column) skips rows where that column is NULL
c) COUNT(*) skips NULL rows
d) COUNT(column) counts distinct values only
Q8. A relation is in First Normal Form (1NF) if:
a) It has no partial dependencies
b) Every attribute holds atomic (indivisible) values
c) It has no transitive dependencies
d) Every determinant is a candidate key
Q9. Removing partial dependencies of non-key attributes on part of a composite key brings a relation to:
a) 1NF
b) 2NF
c) 3NF
d) 4NF
Q10. A relation is in BCNF when:
a) It is in 1NF only
b) For every non-trivial functional dependency X -> Y, X is a super key
c) It has no NULL values
d) It has exactly one candidate key
Q11. In ACID, the 'I' (Isolation) means:
a) Data is stored on an isolated disk
b) Concurrent transactions do not see each other's intermediate results
c) A transaction runs completely or not at all
d) Committed data survives crashes
Q12. Which property guarantees that once a transaction is committed its changes survive a system crash?
a) Atomicity
b) Consistency
c) Isolation
d) Durability
Q13. A dirty read happens when a transaction:
a) Reads data that another transaction has written but not yet committed
b) Reads the same row twice and gets the same value
c) Reads data from a deleted table
d) Reads an index instead of the table
Q14. Which SQL statement correctly finds the second-highest salary from table Emp(salary)?
a) SELECT MAX(salary) FROM Emp WHERE salary < (SELECT MAX(salary) FROM Emp);
b) SELECT salary FROM Emp WHERE salary = 2;
c) SELECT SECOND(salary) FROM Emp;
d) SELECT MAX(salary) - 1 FROM Emp;
Q15. Which of these is a DCL (Data Control Language) command?
a) SELECT
b) ALTER
c) GRANT
d) UPDATE
Q16. An index on a column mainly improves:
a) The speed of INSERT statements
b) The speed of searching and filtering on that column
c) Data integrity
d) Normalization
Recommended MCQs
Comments
Post a Comment