Top 50 Database Interview Questions with Answers

Database interview questions frequently centre on subjects like SQL queries, normalisation, indexing, and data integrity to evaluate a candidate’s knowledge of database management systems. To show their competence, candidates might be asked to optimise queries, solve real-world problems, or describe ideas like joins transactions and ACID features.

Introduction

SQL Server is a user-friendly and easy-to-operate tool for various applications. Its database Engine is its central and essential component, controlling data processing, storage, and, most importantly, data security. The engine facilitates several functions, including data integration, analytics, and transaction processing.

Database Engine provides advanced and sophisticated features to manage the database quickly and adequately, such as indexing, query storage, query optimisation, and transaction management, to ensure optimal speed and data integrity.

A few types of SQL Server Database Engine:

Relational Engine: Manages indexing, transactions, and query processing.

Storage Engine: Controls page allocation, data retrieval, and storage.

Performance is improved for high-concurrency workloads by the in-memory OLTP engine.

Basic Database Interview Questions & Answers

Q: What distinguishes TRUNCATE from DELETE, please?

Ans: DELETE: It can be undone and eliminates rows according to a condition.
Truncate: Deletes every row in a table; as it doesn’t record the deletion of individual rows, it cannot be undone.

Q: What is an index, please?

Ans: By facilitating speedy data lookup, an index enhances query performance. An index enhances query performance by facilitating speedy data lookup. SQL Server has two types of indexes: clustered and non-clustered.

Q: A Stored Procedure: What Is It?

Ans: A stored procedure is a precompiled set of one or more SQL statements that perform particular operations and can accept parameters.

Q: What distinguishes a function from a stored procedure?

Ans: Stored Procedure: This can carry out operations such as altering data and returning several values.
Function: Cannot change database state; returns a single value.

Q: What does the DBCC command accomplish?

Ans: The Database Console Commands (DBCC) are utilized for performance optimization, validation, and maintenance. For instance, DBCC CHECKDB verifies the database’s integrity.

Q: What is an SQL Server Agent, please?

Ans: The SQL Server Agent component helps schedule and automate job executions, backups, and alarms.

Q: What does normalization mean?

Ans: The practice of arranging database tables to minimize dependencies and redundancies is known as normalization.

Q: What distinguishes HAVING clauses from WHERE clauses?

Ans: WHERE: Before grouping, rows are filtered.
HAVING: After aggregation, filter groupings.

Q: What is meant by a deadlock?

Ans: When two or more transactions block one another by retaining a resource the other transaction requires, this is known as a deadlock.

Q: What are the qualities of ACID?

Ans: Atomicity: Guarantees that a transaction’s activities are either finished or not.
Data integrity is maintained by consistency.
Isolation: Each transaction runs on its own.
Durability: Guarantees that finished transactions are preserved indefinitely.

Q: What is a temp table?

Ans: The answer is that temporary tables hold interim data while a query runs and are removed after the session.

Q: How can SQL Server performance be enhanced?

Ans: Utilize indexing, optimize searches, divide data, avoid pointless cursors, and ensure you have enough hardware resources.

Q: What are Common Table Expressions, or CTEs?
Ans: CTEs are short-term result sets that make complicated searches easier to understand and more readable.

Q: What is SQL Profiler, please?

Ans: SQL Profiler is a helpful tool for solving performance issues and monitoring and analyzing SQL Server activity.

Q: What does SQL Server’s Fill Factor mean?

Ans: When creating or rebuilding an index, the fill factor dictates how much space should be left on each page.

Q: What distinguishes mirroring from log shipping?

Ans: Log Shipping: Automates restoring and backing up data between servers.
Mirroring: Offers failover and replication of databases in real-time.

Q: What are sparse columns?

Ans: Sparse columns maximize storage for null values in a table.

Q: SQL Server Always On: What Is It?

Ans: Always On is a high-availability solution that uses Availability Groups to guarantee constant database availability.

Q: In SQL Server, what is a database engine?

Ans: A database engine is the primary tool for processing, storing, and protecting data. It facilitates data integration, analytics, and transaction processing.

Q: What are the significant differences between the Storage and Relational engines?

Ans: The storage engine manages data storage and retrieval, whereas the Relational Engine handles query processing and optimization.

Q: What are SQL Server indexes, and what is their significance?

Ans: Indexes increase the speed at which data can be retrieved by offering fast access routes to rows.

Q: Describe how clustered and non-clustered indexes differ from one another.

Ans: Compared to non-clustered indexes, which preserve a distinct structure referring to data rows, clustered indexes specify the order in which data is stored in a table.

Q: The Query Optimizer in MS SQL Server used for.

Ans: It creates the query’s most effective execution strategy.

Q: In SQL Server, define a transaction.

Ans: To guarantee data consistency, a transaction is a set of actions completed as a single unit of work.

Q: What does SQL Server’s ACID property mean?

Ans: Atomicity, Consistency, Isolation, and Durability—abbreviated ACID—ensure dependable transactions.

Q: How does SQL Server handle concurrency?

Ans: SQL Server employs isolation layers, row versioning, and locking to control concurrency.

Practical-Based Database Interview Questions & Answers

Q: How do you create an index in SQL Server?

Ans: We can use the below command to create an index on a table.

CREATE INDEX ON TableName(ColumnName);

CREATE INDEX NCI_Students_StudentName ON Students(StudentName);

Q: Write a query to optimize a slow-running SELECT statement.

Ans: Use indexing, avoid SELECT *, and analyze execution plans. Example:

SELECT Column1, Column2, Column3, ……., ColumnN
FROM TableName WHERE Condition(s);

Q: How can you configure SQL Server memory settings?

Ans: Use SQL Server Management Studio (SSMS) under Server Properties > Memory.

Q: Demonstrate how to take a full database backup.

Ans: Use the below command to take the database backup:

BACKUP DATABASE TO DISK = 'Path for db backup file' WITH Stats = 5, COMPRESSION;

Q: Explain how to shrink a database using SQL Server Management Studio.

Right-click on the database -> Select Tasks -> Shrink -> Select Database or File -> Select options as needed.

Conclusion

One robust and flexible key element of Microsoft SQL Server is the SQL Server Database Engine. Database developers and administrators must know how to use it well and be familiar with troubleshooting and best practices. Using these interview questions in advance guarantees that you have a solid understanding of the fundamental ideas and valuable abilities needed to succeed in SQL Server positions.