Question 1

What is the difference between SQL and NoSQL databases?

Accepted Answer

The distinction is less about query language than about what the database guarantees and what shape of data it is optimised for.

Relational databases store data in tables with a fixed schema and enforce relationships between them. That enforcement is the point: the database refuses to store a row referencing something that does not exist, refuses to violate a uniqueness rule, and can update several tables atomically. Correctness is the database responsibility rather than the application.

NoSQL covers several quite different families. Document stores keep flexible, nested records. Key-value stores map identifiers to values very fast. Wide-column stores handle enormous tables across many machines. Graph databases model relationships as first-class. Grouping them under one name obscures more than it reveals.

What they generally share is relaxing some relational guarantees in exchange for flexibility or scale. A flexible schema means adding a field requires no migration, which suits rapidly changing data. Distributing across machines is often easier because the data model avoids joins.

The trade-off is that responsibility moves to the application. Without enforced relationships, nothing prevents an orphaned reference. Without a schema, two records can disagree about what a field means, and code must handle both. These problems arrive later than the initial productivity gain, which is why they are frequently underestimated.

The practical guidance is unfashionable but holds: for most applications a relational database is the safer default, and modern ones handle nested documents natively, which removes much of the original reason to choose otherwise. Reach for something else when you have a specific need it serves, such as genuine horizontal scale or a graph-shaped problem.

Question 2

What are the best practices for using GraphQL with React?

Accepted Answer

Implementing best practices for GraphQL with React enhances performance and user experience. Key strategies include using Apollo Client, fragments, optimistic updates, and effective error handling.

Question 3

What does ACID mean in databases?

Accepted Answer

ACID names four guarantees a database provides around transactions. Atomicity means all or nothing. A transaction that updates several rows either applies completely or leaves no trace. A crash

Question 4

What is an ORM, and when should you not use one?

Accepted Answer

An ORM — object-relational mapper — translates between the objects in your program and the tables in a relational database, so you write method calls instead of SQL. What it gives you: Less

Question 5

What techniques can I use to tune the performance of MongoDB?

Accepted Answer

MongoDB performance tuning techniques include indexing, sharding, schema design, connection pooling, query optimization, and hardware optimization. Each method enhances database efficiency and responsiveness.

Question 6

What is a hash table, and why is lookup constant time?

Accepted Answer

A structure that turns a key into an array index by computing a number from it, so finding an item takes roughly the same time whether the table holds ten entries or ten million. The mechanism. A

Question 7

What is eventual consistency?

Accepted Answer

Eventual consistency is a guarantee that, if no new updates are made, all replicas of a piece of data will eventually converge on the same value. It does not guarantee when, and it permits reads that

Related Questions