Interview Questions Answers in Programming Languages AllOther, Database Management, Web Related, SQL PLSQL

What is a programming language?

Answer

o A programming language is a formal language comprised of instructions used to produce various kinds of output, primarily used to control the behavior of a computer.

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Question { 1040 }

What is the difference between compiled and interpreted languages?

Answer

o Compiled languages (e.g., C, C++) are translated into machine code by a compiler before execution.
o Interpreted languages (e.g., Python, JavaScript) are executed line-by-line by an interpreter without pre-compilation.

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Question { 1057 }

What are data structures?

Answer

o Data structures are ways of organizing and storing data to enable efficient access and modification. Examples include arrays, linked lists, stacks, queues, hash tables, and trees.

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Question { 1006 }

What are the main principles of OOP?

Answer

o Encapsulation: Wrapping data and methods that operate on the data into a single unit (class).
o Inheritance: Acquiring properties and behaviors from a parent class.
o Polymorphism: Performing a single function in multiple ways.
o Abstraction: Hiding the implementation details and exposing only the necessary features.

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Question { 1327 }

What is Big-O notation?

Answer

o Big-O notation describes the performance or complexity of an algorithm in terms of the size of the input. Common examples:
 O(1)O(1): Constant time
 O(n)O(n): Linear time
 O(log⁡n)O(log n): Logarithmic time
 O(n2)O(n^2): Quadratic time

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Question { 978 }

Explain recursion with an example.

Answer

o Recursion is a technique where a function calls itself to solve smaller sub-problems.
8. def factorial(n):
9. if n == 1:
10. return 1
11. else:
12. return n * factorial(n - 1)
13. print(factorial(5)) # Output: 120

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Question { 1124 }

What is the difference between SQL and NoSQL databases

Answer

o SQL (Structured Query Language): Relational databases (e.g., MySQL, PostgreSQL) use structured tables.
o NoSQL: Non-relational databases (e.g., MongoDB, Cassandra) store data in flexible, schema-less formats like JSON.

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Question { 768 }

would you design a URL shortening service?

Answer

• Components:
o Frontend to accept long URLs and display short ones.
o Database to store mapping of short URLs to long URLs.
o Backend service to generate short URLs (e.g., using hashing).
o Caching for faster access to frequently accessed URLs.

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Question { 1363 }

What is a primary key, and how is it different from a unique key?

Answer

• Primary Key:
o Ensures each row in a table is unique.
o Cannot contain NULL values.
o A table can have only one primary key.
• Unique Key:
o Ensures all values in a column are unique.
o Can contain a single NULL value.
o A table can have multiple unique keys.

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Question { 1463 }

How do you retrieve the second highest salary from a table?

Answer

Using a subquery:
SELECT MAX(salary)
FROM employees
WHERE salary < (SELECT MAX(salary) FROM employees);
Using ROW_NUMBER():
SELECT salary
FROM (
SELECT salary, ROW_NUMBER() OVER (ORDER BY salary DESC) AS row_num
FROM employees
) ranked
WHERE row_num = 2;

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Question { 1692 }

What is the difference between DELETE, TRUNCATE, and DROP?

Answer

• DELETE:
o Deletes specific rows from a table.
o Can have a WHERE clause.
o DML command (can be rolled back).
• TRUNCATE:
o Deletes all rows from a table.
o Faster than DELETE (does not log individual row deletions).
o DDL command (cannot be rolled back).
• DROP:
o Removes a table entirely (schema + data).
o DDL command.

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Question { 1523 }

What are indexes, and what are the different types?

Answer

Indexes improve query performance by speeding up data retrieval.
Types of Indexes:
1. Clustered Index: Sorts and stores data physically in the table.
2. Non-clustered Index: Creates a separate structure to store pointers to the actual data.
3. Unique Index: Ensures all values in a column are unique.
4. Composite Index: Includes multiple columns in the index.

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Question { 1427 }

Explain the concept of normalization.

Answer

Normalization is the process of organizing data to minimize redundancy and improve data integrity.
Normal Forms:
• 1NF: Eliminate repeating groups, ensure atomicity.
• 2NF: Ensure 1NF and remove partial dependencies.
• 3NF: Ensure 2NF and remove transitive dependencies.
• BCNF: Ensure every determinant is a candidate key.

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Question { 1377 }

What is a CTE (Common Table Expression), and how is it different from a subquery?

Answer

• CTE: Temporary result set defined using WITH and reusable within the query. Improves readability for complex queries.
• Subquery: Nested query executed each time it is called. Example:
WITH SalesCTE AS (
SELECT employee_id, SUM(sales) AS total_sales
FROM sales
GROUP BY employee_id
)
SELECT * FROM SalesCTE WHERE total_sales > 5000;

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Question { 1535 }

What are triggers, and when would you use them?

Answer

A trigger is a block of PL/SQL code automatically executed in response to certain events (e.g., INSERT, UPDATE, DELETE) on a table.
Example Trigger:
CREATE OR REPLACE TRIGGER EmployeeAudit
AFTER INSERT ON employees
FOR EACH ROW
BEGIN
INSERT INTO audit_log(employee_id, action, action_date)
VALUES (:NEW.id, 'INSERT', SYSDATE);
END;

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