Top SQL Interview Questions and Answers for Freshers in 2025.
SQL or Structured Query Language is that skill a data professional needs to have, and most companies are hiring for Data Analysts, Database Administrators, Software Developers, etc. To make sure that freshers attending Top SQL Interview Questions and Answers for Freshers in 2025 should be aware of basics, the commonly asked questions, and the format of answers. Below are some of the critical SQL interview questions and answers from which freshers can expect in the year 2025. The questions are broadly divided into SQL basics, database concepts, and some advanced topics which are sure to guarantee success for freshers.
SQL stands for Structured Query Language, and it is the standard language to use when managing and manipulating relational databases. It is of paramount importance because it allows businesses to query, update, and manage data in a database. This is really important because it enables businesses to deal with high volumes of information in the most effective way possible. Its simplicity, standardization, and integration with most database systems have made SQL universally applied.
1. SQL vs. MySQL: What's the difference?
SQL is an entire language with which one accesses databases, while MySQL is a relational database management system, or RDBMS, which also supports SQL as its language. Summary:
SQL is a language to query databases.
MySQL is the database software that supports SQL.
Primary Key: to each entry in a table, an identifier- the primary key- is assigned. Keys guarantee there to be no duplicate entries and make sure the integrity of data is guaranteed. A table can only have one primary key.
Foreign Key: According to Bianco, "a column of one table referring or linking to a primary key in another." This, thus, creates a relationship between these two tables and ensures referential integrity in place.
A main and foreign key are central because they allow the setting of the relationships that are between tables. This means relating and handling information can be easier coming from different tables.
2. What is normalization? Define its types.
Answer:
Normalization refers to the approach of arranging data in the database, thereby avoiding redundancy of data and maintaining integrity of data. A set of operations, which try to break down a database into tables and then develop connections in such a manner that no redundancy develops.
Types of normalization are as follows:
1NF (First Normal Form): It eliminates redundant columns and applies atomicity, that is, one value per column.
2NF (Second Normal Form): This expands 1NF and eliminates repeating groups of information that appear as many rows with different tables that have separate columns.
3NF (Third Normal Form): This satisfies the 2NF and removes non-keyed columns.
BCNF (Boyce-Codd Normal Form): This is a stronger version of 3NF, wherein every determinant is a candidate key.
3. Explain different types of SQL joins.
Answer:
SQL supports joining records from two or more tables. The following are common types of joins that are explained in the following paragraphs:
INNER JOIN : Returns all records from both tables where there is a match in both.
LEFT JOIN (or LEFT OUTER JOIN): Retrieves all records from the left table and the matched records in the right table. For each record that does not have a match, NULL is returned in the right table columns.
RIGHT JOIN (or RIGHT OUTER JOIN): Returns all records from the right table, along with the matching records from the left table.
FULL JOIN (FULL OUTER JOIN): Returns records where there is a match in either left or right tables, and fills unmatched rows with NULLs.
CROSS JOIN: Returns the Cartesian product of both tables (all combinations of records).
4. What is a subquery in SQL?
Answer:
A subquery is a query nested inside of another query. It helps to perform the operation in stages or to filter records based on the output of another query. Subqueries appear in the SELECT, FROM, WHERE, or HAVING clauses and are divided into the following types:
Correlated Subquery: It is dependent on the outer query and is read row by row.
Non-Correlated Subquery: The subquery is independent of the outer query and gets evaluated once.
5. How does the GROUP BY clause work? Give an example.
Answer:
The GROUP BY clause is used to group the records of having the same values in specific columns. It's mainly utilized with aggregate functions like COUNT, SUM, AVG, etc. for performing the group-by calculations.
Example:
SELECT department, COUNT(employee_id) AS employee_count FROM employees GROUP BY department;
This query counts the number of employees in each department.
A stored procedure is a group of SQL statements that can be saved and reused. Stored procedures encapsulate complex SQL logic, reduce network traffic by improving performance, and protect data through user access controls.
6. What's the difference between DELETE, TRUNCATE, and DROP?
DELETE: delete. Deleting rows can be rolled back if part of a transaction.
TRUNCATE: It deletes all rows in a table without logging individual row deletions. It is not possible to roll back.
DROP : The entire table or database gets deleted with all its data and structure. Not possible to roll back.
7. What are indexes in SQL? Which of the following statements relate to indexes and how they improve the performance?
An index is a kind of special lookup table that allows rows to be retrieved by constructing pointers to data in a table. It ensures access to the data is even faster than usual since the database does not need to scan the whole table to find some specific information. INSERT, UPDATE, and DELETE operations are likely to become slower on the other side because any change to data will launch an update of the index.
8. What is SQL injection, and how can it be avoided?
Answer:
SQL injection is a method to inject malicious SQL code into the query to access or modify the database. To avoid it:
Use parameterized queries or prepared statements.
Validate and sanitize user inputs.
Limit the permissions of the database.
9. How do you retrieve the top N rows from a table?
Answer:
The following syntax can vary depending on the database being used:
MySQL/PostgreSQL: Use LIMIT clause.
SELECT * FROM employees ORDER BY salary DESC LIMIT 5;
SQL Server: Use TOP clause.
SELECT TOP 5 * FROM employees ORDER BY salary DESC;
10. What is a view, and how does it differ from a table?
Answer:
A view is a virtual table constructed based on a query. Unlike a table, the view itself doesn't store data but shows how data can be viewed in one or more tables. Unlike a table, a view does not hold data in some kind of container and therefore will automatically change when a data alteration occurs on an underlying table.
Conclusion
Good luck with SQL interview prep. Again, though, you are not memorizing but understanding concepts since most interviewers want the ability to break down and solve, rather than to know what answer to write. Practice the following questions, then build your confidence in SQL. Good luck!
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