Quark Placement Paper -: SQL Questions With Answers

Quark Previous Years Solved Sample Placement Papers

1. Q12) What is normalization?
   Normalization is the process of organizing data in a database to reduce redundancy and improve data integrity.
   It involves breaking down data into smaller, more manageable tables.
   
   • Helps in reducing data redundancy by eliminating duplicate data.
   • Ensures data integrity by enforcing relationships between tables.
   • Includes levels such as 1NF, 2NF, 3NF, and BCNF.

   A. Reduces redundancy

   B. Improves integrity

   C. Organizes data into smaller tables

   D. All of the above Answer: Option D

2. Q13) What is a correlated subquery?
   A correlated subquery is a subquery that references a column from a table in the outer query.
   
   • Executed for each row processed by the outer query.
   • Used to filter results based on values from the outer query.
   • Example: SELECT * FROM table1 WHERE column1 = (SELECT MAX(column2) FROM table2 WHERE table1.id = table2.id).

   A. Simple subquery

   B. Correlated subquery Answer: Option B

   C. Aggregation query

   D. None of the above

3. Q14) How is useref used?
   useref is used to access the DOM nodes or state values of child components in a parent component.
   
   • Returns a mutable ref object.
   • Accesses the DOM nodes of child components.
   • Accesses state values of child components in a parent component.
   • Example: const childRef = useRef(); childRef.current.doSomething();

   A. For state management

   B. For accessing DOM nodes Answer: Option B

   C. For data fetching

   D. None of the above

4. Q15) Why do we use public, private, and protected?
   Public, private, and protected are access modifiers used to control the visibility of class members in object-oriented programming.
   
   • Public: Allows access to the member from outside the class.
   • Private: Restricts access to the member only within the class.
   • Protected: Allows access to the member within the class and its subclasses.

   A. Control access

   B. Restrict access

   C. Both A and B Answer: Option C

   D. None of the above

5. Q16) What are the types of normalization?
   Normalization is a process of organizing data in a database to reduce redundancy and dependency.
   
   • First Normal Form (1NF)
   • Second Normal Form (2NF)
   • Third Normal Form (3NF)
   • Boyce-Codd Normal Form (BCNF)
   • Fourth Normal Form (4NF)
   • Fifth Normal Form (5NF) or Project-Join Normal Form (PJNF)

   A. 1NF, 2NF

   B. 3NF, BCNF

   C. 4NF, 5NF

   D. All of the above Answer: Option D

6. Q17) Difference between various SQL joins?
   SQL joins are used to combine rows from two or more tables based on a related column between them.
   
   • INNER JOIN: Returns rows when there is at least one match in both tables.
   • LEFT JOIN: Returns all rows from the left table and matching rows from the right table.
   • RIGHT JOIN: Returns all rows from the right table and matching rows from the left table.
   • FULL JOIN: Returns rows when there is a match in one of the tables.
   • CROSS JOIN: Returns the Cartesian product of the two tables.

   A. INNER JOIN

   B. FULL JOIN

   C. CROSS JOIN

   D. All of the above Answer: Option D