Interview Questions and Answers

I have used the Singleton design pattern in my previous projects.

• Used to ensure a class has only one instance and provides a global point of access to it

• Helps in managing global resources efficiently

• Example: Database connection manager in a web application

Primary key is a unique identifier for each record in a database table.

• Primary key ensures each record in a table is unique

• It can be a single column or a combination of columns

• Primary key values cannot be NULL

• Example: 'ID' column in a 'Users' table

Foreign key is a field in a database table that links to a primary key in another table.

• Foreign key ensures referential integrity between related tables

• It helps maintain relationships between tables

• Foreign key constraints can be used to enforce data integrity

A unique key is a field or combination of fields in a database table that uniquely identifies each record in the table.

• A unique key ensures that no two records in a table have the same values for the specified key fields.

• It can be a single field or a combination of multiple fields.

• Unique keys are used to enforce data integrity and prevent duplicate records.

• Examples: Primary key, Unique constraint

Different types of databases include relational, NoSQL, graph, and document databases.

• Relational databases store data in tables with rows and columns (e.g. MySQL, PostgreSQL)

• NoSQL databases are non-relational and can handle unstructured data (e.g. MongoDB, Cassandra)

• Graph databases use graph structures for semantic queries (e.g. Neo4j, Amazon Neptune)

• Document databases store data in documents (e.g. Couchbase, Firebase)

Processes are independent entities while threads are lightweight sub-processes within a process.

• Processes have their own memory space while threads share the same memory space within a process.

• Processes are heavyweight in terms of resources while threads are lightweight.

• Processes communicate with each other through inter-process communication mechanisms like pipes or sockets, while threads can communicate directly through shared memory.

• Example: A web browser running multiple ...read more