Top SQL Interview Questions for Freshers [2025]

I have prepared a complete list of 15 basic SQL interview questions and answers to help you crack the interviews for your dream career. I have picked these basic SQL interview questions carefully, taking help from industry experts depending on what might be asked in upcoming interviews. 

Read this article thoroughly and increase your chances of impressing interviewers with stunning answers. This blog post will offer you a solid and in-depth understanding of SQL. 

Let’s begin this, 

Q1.  Do you think SQL supports the feature of programming language?

However, SQL fails to include all programming language features; it does support some programming languages. Composing queries for connecting with databases has been rendered by it. While it lacks features such as complex control flow and object-oriented programming, it does have statements and conditions, variables, and loops in some versions. It is not mainly employed for developing applications but instead for handling real-time data.

Q2.  What is data manipulation language? 

A subset of SQL is referred to as Data Manipulation Language (DML), which is specially employed to handle complex data in databases. Data selection, updation, insertion, and deletion all come under its major functions. The various DML commands that are used widely are SELECT, UPDATE, INSERT, and DELETE. These commands help the developer in retrieving and modifying the stored data from the database.

Q3.  What is meant by data definition language?

Data Detection Language, commonly known as DDL, refers to a subset of SQL. It helps in managing and detecting the structures of SQL. You can get commands such as ALTER, CREATE, tRUNCATE, and DROP in DDL. Such commands enable you to make, adjust, or delete tables, schemas, or different types of objects in a database.  

Q4. What is a foreign key?

A section, or set of columns, in one table that renders a column in another table easily trackable is known as a foreign key. This key helps you link a primary key of a table with another key known as a foreign key of another table. The primary function is to make the link between two tables. In order to manage continuity between related tables, the foreign key only allows values that can be found only in the mentioned table.

Q5.  What do you mean by normalization?

The process of organizing data in a database to boost data integrity and eliminate redundancy is referred to as normalization. It involves splitting up big tables into tiny, easy-to-manage ones and building links among them. This process ensures that the database is more functional and easier to manage by deleting data that are duplicates. Each one of the different standard forms, 1NF, 2NF, and 3NF, has its distinct set of standards for data arrangement.

Q6. What do you mean by primary key?

The primary key of a database’s table acts as a distinct code for each record. Duplicate data entries are eliminated, and each row is ensured to be individually detected. The primary key should not have NULL values and should possess unique values. In order to offer each table column a different identity, it is usually built on a group of columns or columns.

Q7. How do you differentiate the CHAR and VARCHAR2 datatype in SQL?

The strings that have fixed lengths are stored in the type of datatype referred to as CHAR, which generally allows a specific amount of storage for each value. For example, a  CHAR(10) column will typically use ten characters and pad shorter strings with storage. However, VARCHAR2 is highly functional and beneficial at saving text of various lengths as it generally uses the space needed for the string and collects strings that are of different lengths.

Q8. What do you mean by Auto Increment?

The Auto Increment function of SQL refers to the one that generates a specific value for a column automatically. There is no requirement to set unique values clearly as the value for the auto-incremented column is set to the next number automatically every time a new row is included in the column. Generating different identifiers for each record in a database is rendered simply with this advanced functionality.

Q9. Describe the topic of SQL injection.

When an attacker is able to change or modify SQL queries in a way that enables them to get free access to a database without needed authorization, it is referred to as SQL injection. Malicious code is often entered into inadequately cleaned input fields, like login forms and search boxes, to achieve this. It can result in the loss, unauthorized changes, or loss of sensitive data. Try to use readymade or pre-built statements and input validation to prevent the SQL injection from occurring.

Q10. What do you mean by a T-SQL?

The term T-SQL is referred to as a vital extension of SQL used commonly by Microsoft SQL servers. It boosts normal SQL with programming features such as loops, conditional statements, and variables. Developers can build advanced and functional database procedures, queries, and functions with the help of T-SQL. By providing error-handling, control-of-flow features, and transaction management, it boosts the overall functionality of SQL.

Q11.  State the difference between SQL and PL/SQL. 

The most popular query language, referred to as SQL, helps to handle and work with the numerous data of databases. The major functions include data updation, querying, and data insertion. PL/SQL refers to a popular extension of SQL that Oracle uses widely. It offers SQL programming features such as error management, loops, and conditions handling, allowing programmers to develop more complex and successful scripts, functions, and processes.

Q12. What do you mean by user-defined functions?

Personalized functions made by users to carry out specific database tasks are referred to as user-defined functions or UDFs. SQL or other programming languages, like T-SQL or PL/SQL, are employed for coding. User-defined functions have the ability to process data, return a result, and accept parameters for input. By incorporating repeated tasks into repeated tasks, they help in the streamlining of complicated queries and boost the structure and performance of the code.

Q13. How many types of user-defined functions are there, and state each of them.

There are three types of user-defined functions are there in SQL, and they are Scaler user-defined function, Multi-statement user-defined function, and Inline table-vale user-defined function. 

Scalar user-defined function: A scalar user-defined returns a single value like a text, date, or integer. It handles individual data and can be used for a SELECT statement and other queries. For example, it can calculate or modify data and offer a single result for each row.

Multi-statement user-defined function: It is easy to run various SQL statements with a multi-statement user-defined function. It has higher flexibility than a scalar user-defined function, can run complex queries, and returns a single result. Programs needing additional logic or queries are generally the ones which uses it.

Inline table-value user-defined function: An inline table-valued user-defined function refers to the one that returns tables as a result. It acts similarly to a view and has only a single SELECT statement, but it also takes various parameters. It is used when a set of rows rather than a single value should be returned, often for query joining with other rows and tables.

Q14.  What do you mean by a JOIN in SQL? Mention its types.

The JOIN in SQL refers to the element that helps in linking rows from two or more two tables depending on a relevant column. 

The various types of JOINs are;

• INNER JOIN: It returns the records that have similar values in both tables.
• FULL JOIN: It returns all the records when it finds a match in either the right or the left table. 
• RIGHT JOIN: It returns every record in the right table along with matching left table records. 
• LEFT JOIN: It returns every record in the left table along with matching right table records. 

Q15.  What is ETL in SQL?

The full form of ETL is Extract, Transform, and Load. It is generally employed to collect vital data from various reliable sources, convert it into a usable format, and upload it to a specific data warehouse or database.

The extract is used to pull data from different sources, whereas the transform is used to clean, convert, and filter data, and Load is used to store the transformed data in the specific database for reporting and thorough analysis.