In this era of cutting-edge technology, software developers are turning to SQL databases in droves. The demand for good database designers and programmers is growing steadily. To stay up to date, you will need to know the essentials of database design and integration. Here we compiled a list of some of the best SQL interview questions and answers for you.
These SQL interview questions will help not only in clearing a job interview and landing your favorite job but also in enhancing your productivity in daily SQL tasks. Moreover, you can use these questions for self-assessment of your SQL and database skills. Aside from database development, proficiency in database is among the essential skills for a backend developer in 2023.
SQL Interview Questions
Question No. 1: What is DBMS?
A: A database management system (DBMS) is an integrated suite of programs used to create, store, organize, manipulate, and retrieve data in the database.
Question No. 2: What is RDBMS?
A: RDBMS stands for Relational Database Management System. It is a major type of database management system that works by dividing the data into smaller chunks and keeping these chunks separate from each other. This prevents them from being corrupted during the transfer process.
Question No. 3: What is SQL?
A: Structured Query Language (SQL) is a database query language. Data stored in a database is generally organized into tables by columns and rows, and SQL provides commands for creating, altering, and dropping (i.e. deleting) those tables and the data within them.
Question No. 4: What are tables and fields?
A: Tables are the dimensions of our data, while fields are the measures. A table is a grid, pile, or list of information with which you organize your records. A field is a specific type of data in a table.
Field: Class ID, Name
Data: 123456, Rinkal
Question No. 5: What is a primary key?
A: A primary key is a special field used to identify every element in a database table. It is usually implemented by making the field or combination of fields participate in the table’s unique index. This helps to ensure that no two rows in the table have duplicate values for any part of their primary key.
Question No. 6: What is a unique key?
A: A Unique key is a column (or collection of columns) within a relational database table, such that no two rows in any table can be equal to each other. Unique keys are the primary mechanism for enforcing data integrity by preventing duplicate data entries.
Question No. 7: What is a foreign key?
A: A foreign key is used to join two tables together based on a relationship (or key) between certain fields. For example, if you have an employee table (with an employee ID) and an order table (with an order number), the order number might be considered as the foreign key related to the employee ID.
Question No. 8: What is a join?
A: Joins are used to link together data from multiple tables into one single table. With a basic knowledge of SQL joins, information can be extracted from many different sources and viewed in a meaningful way.
Question No. 9: What are the types of SQL joins?
A: There are four types of SQL joins:
- Inner Join – An inner join is a type of join that returns only the rows in the first table that have a corresponding row in the second table.
- Right Join – A right join retrieves the records from the table on the right side of an SQL statement.
- Full Join – In a full join, all possible combinations of rows are returned, ensuring that no data is missing or repeated.
- Left Join – Left joins in SQL are used to return the matches from the left table in a join query.
Question No. 10: What is database normalization?
A: Normalization on a database level means bringing different data sources into a single, uniform structure. A database can have different normalization forms, namely 1NF, 2NF, 3NF, BCNF, 4NF, and 5NF. The primary intent of database normalization is to minimize data redundancy.
Question No. 11: What is denormalization?
A: Denormalization, simply put, is the opposite of normalization. Instead of moving values to separate tables, denormalization regroups previously separated values into the same table, making it all simpler for multiple queries to access that data.
Question No. 12: What is a view in a database?
A: A view is an abstraction of the data. Instead of showing all the data, views provide some specific kind of output based on user-defined criteria.
Question No. 13: What is an index?
A: An index is a structure that allows you to quickly retrieve information that has been indexed. It is just another table listed with all the indexes that a specific database has available.
Question No. 14: What is a cursor?
A: A cursor is a way of controlling access to tables in SQL. Though it is hard to appreciate the full power of cursors without working through some practical examples, they can be surprisingly useful. A cursor allows you to programmatically control the order in which SQL processes the data.
Question No. 15: What is a query?
A: A query is a declarative statement that tells the computer what record or records you want. A query can be an SQL statement that is executed by the computer, or it can be a user-defined report that is displayed to the users through some kind of graphical interface.
Question No. 16: What are other popular types of database management systems than relational databases?
A: There are several types of database management systems. However, not all enjoy the same level of popularity as relational databases. Nonetheless, some are popular and give good competition to RDBMSs. These include NoSQL, document-oriented, and object-oriented databases.
A popular example of a NoSQL database is MongoDB. Unlike relational databases, it doesn’t require a predefined schema and it can store unstructured data. This makes MongoDB extremely useful for Big Data purposes. Moreover, MongoDB powers both MERN and MEAN stacks.
That rounds up our list of the best SQL interview questions in 2023. The purpose of this blog post is to give a good sense of the different types of questions you will encounter in a SQL interview and to provide a list of questions that you can practice.
We do not claim that these are the only questions you’ll see in your interview, nor would we say that if you know all these, you will pass your interview with flying colors. However, these SQL interview questions and answers will give you an idea about the questions that you might face during a SQL developer or related job interview.
The best approach to prepare for a SQL or database interview is to familiarize you with common SQL terms and functions, create test databases to run these functions with realistic data sets, and understand the inner workings of SQL queries.