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23 Databases interview questions and answers for software engineers

A database is an organized collection of data, generally stored and accessed electronically from a computer system. Where databases are more complex they are often developed using formal design and modeling techniques. Here is a list of coding interview questions on Databases to help you get ready for your next data structures interview in 2021.

1.

What is Normalization?

Answer:

It is the process of eliminating redundant data and maintaining data dependencies.

Source: github.com/dhaval1406   
2.

What are the advantages of NoSQL over traditional RDBMS?

Answer:

NoSQL is better than RDBMS because of the following reasons/properities of NoSQL:

  • It supports semi-structured data and volatile data
  • It does not have schema
  • Read/Write throughput is very high
  • Horizontal scalability can be achieved easily
  • Will support Bigdata in volumes of Terra Bytes & Peta Bytes
  • Provides good support for Analytic tools on top of Bigdata
  • Can be hosted in cheaper hardware machines
  • In-memory caching option is available to increase the performance of queries
  • Faster development life cycles for developers

Still, RDBMS is better than NoSQL for the following reasons/properties of RDBMS:

  • Transactions with ACID properties - Atomicity, Consistency, Isolation & Durability
  • Adherence to Strong Schema of data being written/read
  • Real time query management ( in case of data size < 10 Tera bytes )
  • Execution of complex queries involving join & group by clauses
Source: stackoverflow.com   
3.

Define ACID Properties

Answer:

  • Atomicity: It ensures all-or-none rule for database modifications.
  • Consistency: Data values are consistent across the database.
  • Isolation: Two transactions are said to be independent of one another.
  • Durability: Data is not lost even at the time of server failure.
4.

What is Denormalization?

Answer:

It is the process of improving the performance of the database by adding redundant data.

Source: github.com/dhaval1406   
5.

What are the difference between clustered and a non-clustered index?

Answer:

  • A clustered index is a special type of index that reorders the way records in the table are physically stored. Therefore table can have only one clustered index. The leaf nodes of a clustered index contain the data pages.
  • A non clustered index is a special type of index in which the logical order of the index does not match the physical stored order of the rows on disk. The leaf node of a non clustered index does not consist of the data pages. Instead, the leaf nodes contain index rows.
Source: github.com/dhaval1406   
6.

How a database index can help performance?

Answer:

The whole point of having an index is to speed up search queries by essentially cutting down the number of records/rows in a table that need to be examined. An index is a data structure (most commonly a B- tree) that stores the values for a specific column in a table.

Source: stackoverflow.com   
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