Top Relational Databases Interview Questions and Answers You Should Learn

Going through the most anticipated Relational Database interview questions is crucial for cracking your tech interview and evaluating your current preparation level. Knowledge of relational databases opens doors to top-rated companies in the US, including Pioneer Hi-Bred International, Bank of America, Verizon, Wells Fargo, Oracle, IBM, Accenture, and others.

The simplicity, flexibility, robustness, scalability, and compatibility of relational databases in managing generic data have led to their dominance in several industries. You can multiply your chances of getting hired at top companies by being adept in the core concepts and the applications of relational databases. The following relational database interview questions will help you brush up on the fundamental and advanced topics.

The Difference Between DBMS and RDBMS

The software used to store, query, manage, and retrieve data from a database is called a database management system (DBMS). When a database management system is based on the relational model, it is referred to as a relational database management system (RDBMS). 

You must understand the difference between DBMS and RDBMS to acknowledge why RDBMS is gaining popularity and has become an important part of interview questions for various companies. The following table lists the key differences between the two.

Commonly Asked Relational Databases Interview Questions and Answers

To consolidate all that you have learned about relational databases, here is a list of the most commonly asked relational database technical questions for the interview.

Q1. Explain the relational database model.

This is one of the most commonly asked relational database interview questions. The relational database model defines the relationship among various databases and their connection. Thus, a relational model represents how data is stored. Some important terms for understanding the relational database model are:

• In an RDB, data is stored in the form of tables. A table is also called a relation.

• Attributes are the properties that define a relation representing columns.

• Relation schema represents the name of the relation with its attributes.

• Rows in a relation are called tuples.

• The set of tuples at a particular instance is called a relation instance. It can be altered with insertion, deletion, or update in the database.

• The total number of attributes/ columns in the relation is referred to as the degree of the relation.

• The total number of rows/ tuples in a relation is its cardinality.

Q2. What do you understand about ACID properties?

ACID stands for the following four crucial properties that define relational database transactions:

• Atomicity represents all the elements that make up a complete database transaction.

• Consistency is about maintaining data points in the right state after a transaction.

• Isolation means that no other process can change the data while a transaction is running. It keeps the effect of a transaction invisible to others until it is committed.

• Durability is the property that ensures that data changes are persistent once the transaction is committed.

Also read: Database Interview Questions.

Q3. What is data redundancy?

Recruiters often ask relational database interview questions on data redundancy and ways to remove the same. Duplication of information is referred to as data redundancy. It is best to eliminate redundancy as far as possible because duplicate information wastes storage space and lowers the database integrity.

Q4. What is Normalization?

Normalization is a data organization process such that it minimizes redundancy. It involves the division of the database into multiple tables and defining logical relationships among them. The different normalizations are 1NF, 2NF, 3NF, 4NF, 5NF, BCNF, ONF, and DKNF.

Q5. What are the types of keys in relational databases?

Keys and their types are often a part of the relational database interview questions. A key is an attribute that helps identify a tuple/ row in a relation/ table. They establish relationships between different tables and columns. Each key has a key value. Following are the different types of keys in a relational database:

• Primary key: It doesn't allow duplicate/ null values and null values. It can be defined at table level or column level. There is only one primary key per table.

• Foreign key: It allows values present in the referenced column only. It can have duplicate/ null values.

• Candidate Key: It is a minimum super key, and there is no proper subgroup of Candidate key attributes. One of all candidate keys is chosen as the primary key.

• Super Key: It is a set of attributes of a relation schema. All attributes of the schema are partially dependent on the super key. Two rows cannot possess the same value of super key attributes.

• Unique Key: It is similar to the primary key except that unique keys allow null values and primary keys do not. So, they are primary keys with null values.

• Alternate Key: The candidate keys that are not chosen as primary keys are alternate keys.

• Composite Key: It combines two or more columns that can uniquely identify each row/tuple in a table.

Q6. What are relational database indexes?

A data structure containing a copy of a column from a database table that increases the speed of retrieval operations on the original column in the table is called an index. The following are the main types of indexes:

• A clustered index is the index at which data is physically stored on the disk, and only one clustered index can be created for a database table.

• A non-clustered index does not define physical data. It tells a logical ordering, such as the B-Tree index.

Q7. What is data abstraction? Explain the levels of abstraction.

You should be prepared for relational databases interview questions on data abstraction as they are amongst the most frequently asked questions. The process of hiding irrelevant details from users is data abstraction. There are three main levels of abstraction:

• Physical level: The lowest level that describes how data is stored in a database.

• Logical level: The next is the logical level which describes what type of data is stored in a database. It also explains the relationship between these data.

• View level: This level is the highest among abstraction levels and describes the entire database.

Q8. Why is Oracle the most popular relational database?

Oracle is always a part of relational database interview questions since it is the most popular RDBMS. It is popular because it has a fully scalable relational database architecture. Oracle database products grant customers high-performance and cost-optimized versions.

The Oracle database offers its own network component that allows communications across networks. Thus it has become the choice of top global enterprises that manage and process data across wide and local area networks.

Also read: Oracle SQL Interview Questions

Relational Database Administrator Interview Questions for Practice

The following database administrator interview questions will help you get familiar with the commonly asked questions you may encounter during an interview.

1. How would you protect a relational database from hacker attacks?

2. What is data warehousing?

3. Why would you prefer RDBMS?

4. Explain the different Codd's 12 rules for Relational Databases.

5. What is a buffer manager?

6. What is your experience in working with cloud databases?

7. What is the significance of Open Database Connectivity or ODBC?

8. What would you do if data loss occurred during data migration?

9. Why is it considered inappropriate to run a test on a live database?

10. When would you prefer the offline backup method over online backup?

Also read: 50+ SQL Interview Questions and Tips on How to Crack Them

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FAQs: Relational Databases Interview Questions

Q1. How do I prepare for relational database interviews?

To prepare for relational database interviews, you must get familiar with the types of questions asked during the technical interview rounds. There can be questions about defining a term, differentiating, elucidating functions, and solving or writing queries. 

Q2. What job positions entail knowledge of relational databases interview questions?

If you are gunning for a job as a Database Manager, Data Analyst, Data Scientist, Information Security Analyst, Database Administrator, Data Modeler, or any other Software Engineering position, you should practice relational databases interview questions.

Q3. What are the most popular relational databases?

Top tech companies' most popular relational databases are Oracle, MySQL, SQL Server, PostgreSQL, and SQLite. Facebook uses MySQL as the primary database for storing all the social data, and Amazon prefers Oracle.

Q4. Using relational database interview questions, what skills do top companies look for in database administrators?

Recruiters put across challenging relational database interview questions to gauge your hard and soft skills effectively. You must possess DBA skills, backup, recovery, and proficiency in Scripting/Automation like Perl, Database tools, and OS (Linux/UNIX/Windows/zOS). Thorough knowledge of SQL is also a must. 

Q5. What is the average salary of a database administrator?

The average salary of Database Administrators is $90,199 per annum. While the best-paid 25 percent makes up to $126,890 per year, the lowest-paid 25 percent makes approximately $71,900 per year on average.