🚀 Coding Interview Questions with Answers (Part 17)

1️⃣6️⃣1️⃣ What is an Aggregate Function?
Answer:
An aggregate function performs calculations on a group of rows and returns a single result.
Common Aggregate Functions:
• "COUNT()" – Counts the number of rows.
• "SUM()" – Calculates the total of a numeric column.
• "AVG()" – Returns the average value.
• "MIN()" – Returns the smallest value.
• "MAX()" – Returns the largest value.

Example:
SELECT AVG(Salary)
FROM Employees;

1️⃣6️⃣2️⃣ What is the GROUP BY Clause?
Answer:
The "GROUP BY" clause is used to group rows that have the same values in one or more columns. It is commonly used with aggregate functions to summarize data.

Example:
SELECT Department, COUNT(*)
FROM Employees
GROUP BY Department;

Applications:
• Sales reports
• Employee statistics
• Business analytics

1️⃣6️⃣3️⃣ What is the HAVING Clause?
Answer:
The "HAVING" clause is used to filter grouped records after the "GROUP BY" operation.

Difference:
• "WHERE" filters individual rows before grouping.
• "HAVING" filters groups after grouping.

Example:
SELECT Department, AVG(Salary)
FROM Employees
GROUP BY Department
HAVING AVG(Salary) > 50000;

1️⃣6️⃣4️⃣ What is the Difference Between DELETE, DROP, and TRUNCATE?

Answer:
DELETE
• Removes selected rows.
• Can use a "WHERE" clause.
• Can be rolled back (depending on the transaction).

TRUNCATE
• Removes all rows from a table.
• Cannot use a "WHERE" clause.
• Faster than "DELETE".
• Keeps the table structure.

DROP
• Removes the entire table, including its structure and data.
• The table no longer exists after execution.

1️⃣6️⃣5️⃣ What is Database Optimization?
Answer:
Database optimization is the process of improving database performance to make queries execute faster and use fewer resources.

Techniques:
• Creating indexes
• Writing efficient SQL queries
• Normalization and denormalization
• Query optimization
• Partitioning large tables

1️⃣6️⃣6️⃣ What is an Operating System?
Answer:
An Operating System (OS) is system software that manages computer hardware and software resources while providing services for application programs.

Examples:
• Windows
• Linux
• macOS
• Android
• iOS

Functions:
• Memory management
• Process management
• File management
• Device management
• Security

1️⃣6️⃣7️⃣ What is a Process?
Answer:
A process is a program that is currently being executed. Each process has its own memory space, resources, and execution state.

Characteristics:
• Independent execution
• Own memory allocation
• Managed by the operating system
Example: Running a web browser or text editor.

1️⃣6️⃣8️⃣ What is a Thread?
Answer:
A thread is the smallest unit of execution within a process. Multiple threads within the same process share memory and resources.

Advantages:
• Faster execution
• Better responsiveness
• Efficient resource utilization

Example: A web browser downloading a file while allowing you to browse other pages.

1️⃣6️⃣9️⃣ What is the Difference Between a Process and a Thread?
Answer:
Process
• Independent execution unit.
• Has its own memory space.
• Higher resource consumption.
• Communication between processes is slower.

Thread
• Runs within a process.
• Shares memory with other threads.
• Lower resource consumption.
• Faster communication between threads.

1️⃣7️⃣0️⃣ What is CPU Scheduling?
Answer:
CPU Scheduling is the process of selecting which process or thread should use the CPU next.
Common Scheduling Algorithms:
• First Come First Serve (FCFS)
• Shortest Job First (SJF)
• Round Robin (RR)
• Priority Scheduling
• Multilevel Queue Scheduling

Objectives:
• Maximize CPU utilization.
• Minimize waiting time.
• Improve system responsiveness.
• Increase throughput.

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