Top 50 Essential Database Interview Testing Questions With Answers

Database Interview Testing Questions

In the rapidly evolving world of software development, ensuring the integrity, consistency, and performance of databases is paramount. As a result, database testing has become a critical component of the software testing process. 

In the realm of software development and data management, database testing plays a pivotal role. It ensures data integrity, consistency, and security.

As the demand for robust databases grows, so does the need for proficient database testers. Databases play a pivotal role in storing, managing, and retrieving crucial data.

If you’re gearing up for a role in this domain or looking to hire a skilled professional, familiarizing yourself with essential “database testing interview questions”. These questions can provide a significant edge.

This guide delves into the top questions and insights to help you navigate your next interview or hiring process. In this guide, we delve into the most pertinent questions in this domain, helping you gauge or showcase expertise effectively.

Top 50 Database Testing Interview Questions & Detailed Answers

Top 50 Database Testing Interview Questions & Detailed Answers

These database testing interview questions for testers not only gauge the depth of one’s knowledge but also their practical experience in handling real-world challenges.

As the world becomes more data-driven, the importance of database test strategy in software testing and the professionals behind it will only continue to grow.

These expanded SQL database testing interview questions for freshers and answers provide a deeper understanding of each topic. But it’s always a good idea to be prepared for follow-up questions in an interview setting.

1. What is database testing?

Database testing involves verifying the structural integrity and accuracy of data stored in a database.

It ensures that data operations (insert, update, delete, and retrieve) are performed correctly, and checks for data integrity, consistency, and validation.

2. What are the different types of database testing?

The main types include:

  • Structural Testing: Focuses on table and column integrity, schema, and database server validations.
  • Functional Testing: Validates database functions, triggers, views, and stored procedures.
  • Non-functional Testing: Concentrates on database performance, scalability, and reliability.
  • UAT (User Acceptance Testing): Ensures the database works for the end-user.

3. What is data integrity?

What is data integrity is one of the important database testing interview questions. Data integrity refers to the accuracy, consistency, and reliability of data stored in a database. It ensures that the data remains unaltered and consistent over its lifecycle. 

4. What is a primary key?

A primary key is a unique identifier for a record in a table. It ensures that each record can be uniquely distinguished, and it cannot have NULL values.

5. What is a foreign key?

A foreign key is a column or set of columns in one table that references the primary key columns of another table, ensuring referential integrity.

6. What is normalization?

Normalization is a systematic approach to decomposing tables to eliminate data redundancy and undesirable characteristics like insertion, update, and deletion anomalies.

7. What is denormalization?

Denormalization is the process of adding redundancy to a normalized database to improve read performance. It often involves combining tables or adding redundant columns.

8. What is SQL injection?

SQL injection is a malicious technique where attackers can insert arbitrary SQL code into a query. This can lead to unauthorized viewing of data, corrupting or deleting data, and other unintended outcomes.

9. What is ACID property in a database?

ACID stands for:

  • Atomicity: Ensures that all operations within a transaction are completed successfully; otherwise, the transaction is aborted.
  • Consistency: Ensures that the database remains in a consistent state before and after the transaction.
  • Isolation: Ensures that concurrent execution of transactions leaves the database in the same state as if the transactions were executed sequentially.
  • Durability: Ensures that once a transaction is committed, it remains so, even in the event of crashes.

10. What is a stored procedure?

A stored procedure is a group of SQL statements that forms a logical unit and performs a particular task. Stored procedures are precompiled and stored in the database.

11. What is a trigger?

A trigger is a set of instructions that are automatically executed (or fired) in response to a specific event on a particular table or view in a database.

12. What is a view in a database?

A view is a virtual table that is based on the result-set of an SQL statement. It does not store data physically but rather displays data from one or more tables through a query.

13. What is a join?

A join is an SQL operation that combines rows from two or more tables based on a related column between them.

14. What is the difference between INNER JOIN and LEFT JOIN?

An INNER JOIN returns rows when there is a match in both tables. A LEFT JOIN (or LEFT OUTER JOIN) returns all rows from the left table and the matching rows from the right table. If there’s no match, the result is NULL on the right side.

15. What is a deadlock?

A deadlock occurs when two or more transactions are waiting indefinitely for each other to release resources, creating a standstill.

16. What is data migration testing?

Data migration testing ensures that data is transferred correctly and completely from a source system to a target system, without any data loss or corruption. It validates data integrity, checks for errors, and ensures that all data is accurately migrated.

17. What is a database cursor?

A cursor is a control structure used for the traversal of database records. It allows row-by-row processing for the result set of a query.

18. What is clustering in a database?

Clustering, in the context of databases, refers to the arrangement of data by its similarity.

A clustered index, for instance, reorders the way records in the table are physically stored, ensuring that rows with adjacent index values are stored close to each other.

19. What is a schema?

A schema is a collection of database objects, including tables, views, indexes, and procedures. It acts as a container for these objects and can be used to define namespaces.

20. What is a subquery?

A subquery, also known as an inner query or nested query, is a query embedded within another SQL query. It can return data that will be used in the main query as a condition to further refine the data that is retrieved.

21. What is the difference between DELETE and TRUNCATE commands?

DELETE removes rows from a table based on a condition and logs individual row deletions, which can be rolled back. TRUNCATE removes all rows from a table, resets the table’s identity seed (if it has one), and is more efficient than DELETE, but cannot be rolled back at the row level.

22. What is a database transaction?

A transaction is a sequence of one or more SQL operations treated as a single logical unit. All operations within a transaction are either committed (made permanent) or rolled back (undone) together.

23. What is a data warehouse?

A data warehouse is a large, centralized database that is specifically designed for query and analysis. It consolidates data from different sources, making it accessible for business intelligence activities.

24. What is ETL?

ETL stands for Extract, Transform, Load. ETL testing interview questions are also important. It’s a process used in data warehousing that involves:

  • Extracting data from source systems.
  • Transforming it into a consistent, clean, and usable format.
  • Loading it into a data warehouse or other systems.

25. What is a fact table?

In the context of data warehousing, a fact table contains the quantitative performance measures of the business. It typically contains keys to dimension tables and facts (or measures) like sales amount, quantity sold, etc.

26. What is a dimension table?

A dimension table contains descriptive, textual or categorical information, typically the entry points to data. Examples include time, product, location, and customer dimensions.

27. What is referential integrity?

Referential integrity is a set of rules that DBMS enforces to maintain relationships between tables when records are entered or deleted. It ensures that foreign key values always have corresponding primary key values.

28. What is an index?

An index is a database object that enhances the speed of data retrieval operations on a database table. It provides a pointer to data in a table and is similar to an index in a book.

29. What is the difference between clustered and non-clustered indexes?

A clustered index determines the physical order of data in a table. Each table can have only one clustered index.

A non-clustered index, on the other hand, does not alter the physical order but creates a separate object within the table that points back to the original table rows.

30. What is a database constraint?

Constraints are rules that are applied to table columns to ensure the accuracy and reliability of the data in the table. They enforce the integrity of the data.

31. Name some common database constraints.

Common constraints include:

    • PRIMARY KEY: Uniquely identifies each record in a table.
    • FOREIGN KEY: Ensures referential integrity by creating a link between two tables.
    • UNIQUE: Ensures that all values in a column are unique.
    • NOT NULL: Ensures that a column cannot have a NULL value.
    • CHECK: Validates that data meets a specific condition.

32. What is a query optimizer?

A query optimizer is a component of a database management system that determines the most efficient way to execute a SQL query. It evaluates different query strategies and selects the one with the least estimated cost.

33. What is a database checkpoint?

A checkpoint is a mechanism where all the previous logs are written to the actual database from the buffer memory. It helps in reducing the recovery time in case of system crashes.

34. What is a data mart?

A data mart is a subset of a data warehouse that focuses on a specific business function or department. It’s smaller than a data warehouse and is used to offload queries or to provide data to a specific group of users.

35. What is OLAP?

OLAP stands for Online Analytical Processing. It’s a category of software testing tools that provides analysis of data from multiple dimensions, facilitating complex calculations, trend analysis, and advanced data modeling.

36. What is the difference between a database and a spreadsheet?

A database is designed to store, retrieve, and manage large amounts of structured data efficiently. It supports complex queries and can handle concurrent users.

A spreadsheet, on the other hand, is designed for individual data analysis, calculations, and can represent data in rows and columns visually.

37. What is a relational database?

A relational database is a type of database that organizes data into tables (relations) which can be linked—or related—based on data common to each. This model is based on the relational model introduced by E.F. Codd.

38. What is DDL and DML?

  • DDL (Data Definition Language): Deals with database schemas and structures. Examples include CREATE, ALTER, and DROP.
  • DML (Data Manipulation Language): Deals with data manipulation. Examples include SELECT, INSERT, UPDATE, and DELETE.

39. What is the difference between CHAR and VARCHAR data types?

  • CHAR: It’s a fixed-length character data type. If the length of the string is less than the set length, it will be padded with spaces.
  • VARCHAR: It’s a variable-length character data type. It stores characters up to the defined number but uses only the required amount of storage.

40. What is a self-join?

A self-join is a join where a table is joined with itself. It’s useful when comparing rows within the same table or when the data is hierarchical.

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41. What is a composite key?

A composite key is a type of candidate key that consists of two or more attributes (or columns) to uniquely identify an entity in a table.

The concept of a composite key stands as a fundamental element with far-reaching implications. A composite key represents a dynamic approach to uniquely identify entities within a table.

Unlike a conventional primary key, which relies on a single attribute for identification, a composite key takes the complexity up a notch. It entails the fusion of two or more attributes.

42. What is data redundancy?

Data redundancy occurs when the same piece of data is stored in multiple places in a database. It can lead to inconsistencies and can waste storage space.

Data redundancy emerges as a concept with both practical and potential pitfalls. At its core, data redundancy refers to the occurrence of the same piece of data being stored in multiple locations within a database.

While this might seem like a harmless occurrence, it carries significant implications that warrant careful consideration. Each instance of the address represents a separate occurrence of the same data. 

43. What is a database view?

A database view is a virtual table that provides a way to view and access a subset of the database’s data, possibly from multiple tables, in a single logical table.

44. What is the difference between UNION and UNION ALL?

  • UNION: Combines the result sets of two or more SELECT statements and removes duplicates.
  • UNION ALL: Combines the result sets of two or more SELECT statements and retains duplicates.

45. What is a database lock?

A database lock is a mechanism used by a DBMS to ensure that multiple transactions can’t access the same data simultaneously in a way that would compromise data integrity.

46. What is a correlated subquery?

A correlated subquery is a subquery that references columns from the outer query. It’s executed repeatedly, once for each row selected by the outer query.

47. What is a BCP utility in databases?

BCP (Bulk Copy Program) is a command-line utility in databases like SQL Server. It’s used for the import/export of large amounts of data from tables and views between databases or from external files.

48. What is the difference between a logical and physical database model?

A logical database model describes the logical attributes and structures designed during the conceptual design phase without any technical details. A physical database model involves concepts such as table structures, column data types, indexes, and more, detailing how the data will be physically stored in the database.

49. What is data profiling?

Data profiling is the process of examining, analyzing, and reviewing data to gather metadata about its quality, consistency, and structure. It helps in understanding anomalies, patterns, and dependencies in the existing data.

50. What is a shard in databases?

A shard refers to a horizontal data partition in a database or search engine. Each shard is held on a separate database server instance, spreading the load and allowing for data to be scaled horizontally.

Bottom Line

Database testing is an indispensable aspect of software quality assurance. The right “database testing interview questions” not only help in identifying the best talent but also ensure that the databases powering our applications are robust, efficient, and free from defects.

Database testing is an integral component of the software development lifecycle. It ensures that databases function as intended and safeguard critical data.

Whether you’re on the hiring side or the job-seeking side, a thorough understanding of these questions will undoubtedly set you on the path to success.

Always remember, it’s not just about knowing the answers. But it’s about understanding the underlying principles and best practices that make a database truly reliable.

Rahnuma Tasnim
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