SQL Interview Questions and Answers- Part 3

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SQL Interview Questions and Answers- Part 3

As your experience grows in tech, employers expect more than just basic SQL knowledge. Mid-level professionals are often asked scenario-based SQL questions that reflect real data challenges, such as performance tuning, complex joins, window functions, and data transformation. This guide compiles the top SQL interview questions aimed at those with 2–5 years of experience.

The questions not only test your syntax but also your ability to write efficient queries, handle large datasets, and optimize database performance. Each answer includes a clear explanation to help you understand the logic and improve your response in technical rounds. If you’re preparing for roles in software development, data engineering, or business intelligence, this list will help you polish your skills and build confidence in solving SQL problems under pressure.

Essential SQL interview questions act as a catalyst for career growth. Candidates are often asked to explain normalization, write queries with subselects, or optimize performance using indexes. These questions test your technical foundation, but employers want more than theoretical answers. They want professionals who can apply SQL in conjunction with modern tools and frameworks.

To succeed, you need to demonstrate proficiency in Power BI, Tableau, SQL, SAS, and Azure. Data engineering skills in Snowflake, Databricks, and PySpark are critical for building scalable pipelines. Employers also expect candidates to have exposure to machine learning and AI frameworks such as TensorFlow, PyTorch, LLMs, and Generative AI. Project work that integrates these skills is often the differentiator in hiring decisions.

The SynergisticIT Data Science Job Placement Program ensures you’re not just prepared for interviews but also for the hybrid nature of modern roles. By combining SQL mastery with advanced frameworks, project-based learning, and interview preparation, SynergisticIT helps you turn your catalyst into a successful career. Explore more through the SynergisticIT Job Placement Program

Answer:

A cross-join, also known as a Cartesian product, is an operation in relational databases and SQL (Structured Query Language) that combines every row from one table with every row from another table. It generates a result set where the number of rows in the output is equal to the product of the number of rows in the two tables being cross-joined.

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In SQL, VARCHAR2 and CHAR are both datatypes used to store character strings. However, they have some differences in terms of storage and behavior:

  1. Storage: VARCHAR2 is variable-length, meaning it can store strings of different lengths. It only uses the necessary amount of storage to store the actual data. On the other hand, CHAR is fixed-length, meaning it always uses the specified amount of storage, regardless of the length of the data stored.
  2. Trailing Spaces: In VARCHAR2, trailing spaces at the end of a string are not automatically removed or ignored. If you store a string with trailing spaces, they will be preserved in the VARCHAR2 column. However, in CHAR, trailing spaces are automatically padded to the specified length. If you store a string with fewer characters than the specified length, it will be padded with spaces to fill the remaining length.
  3. Performance:  Since VARCHAR2 only uses the necessary amount of storage, it can be more efficient in terms of storage space. It is suitable for columns that may have varying lengths and where space efficiency is important. In contrast, CHAR uses a Fixed-length storage that can be more efficient for certain use cases where the data length is consistently the same for all records. It can be faster for operations involving string comparisons and sorting since there is no need to account for variable-length data.

Answer:

SQL injection is a type of security vulnerability that occurs when an attacker inserts malicious SQL code into a query, typically through user input fields such as forms or URL parameters. This vulnerability arises when a web application fails to properly validate or sanitize user input before incorporating it into an SQL statement.

The purpose of a SQL injection attack is to manipulate the structure or behavior of the original SQL query, allowing the attacker to execute unintended commands or retrieve unauthorized data from the database. This can lead to various consequences, including unauthorized access, data breaches, data manipulation, or even the complete compromise of the application or system.

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To prevent SQL injection use secure coding practices, such as parameterized queries or prepared statements, which separate SQL code from user-supplied data and ensure it is properly escaped or sanitized. Additionally, input validation and output encoding can help protect against such attacks by filtering and sanitizing user input and ensuring that it does not contain any malicious code.

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In SQL, the ALIAS command allows you to assign a temporary name or alias to a table or column. It is used to make queries more readable and concise, especially when dealing with complex queries involving multiple tables or columns. By assigning an alias, you can refer to the table or column using the alias name instead of its original name throughout the query. ALIAS can be used in SELECT statements, JOIN operations, and subqueries to improve the clarity and understandability of the code.

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There are several ways to execute dynamic SQL, depending on the programming language or database management system you are using. Here are a few common methods:

  • By using EXEC
  • By using sp_executesql
  • By executing the query with parameters

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In SQL (Structured Query Language), a query is a request for data or action performed on a database. It is used to retrieve, manipulate, or manage data stored in a relational database management system (RDBMS). A query allows you to specify the criteria for selecting, updating, inserting, or deleting data from a database table or multiple tables.

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A recursive stored procedure is a stored procedure that calls itself one or more times during its execution. It allows you to perform repetitive operations or solve complex problems by breaking them down into smaller, manageable tasks.

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In SQL, several functions can be used to manipulate the case of strings. These functions allow you to convert the case of characters in a string to uppercase, lowercase, or title case. Here are some commonly used case manipulation functions in SQL:

  1. UPPER(string): This function converts all characters in the string to uppercase.
  2. LOWER(string): This function converts all characters in the string to lowercase.
  3. INITCAP(string): This function converts the first character of each word in the string to uppercase and the remaining characters to lowercase.

Answer:

The GRANT command is a database operation used to grant specific privileges or permissions to database users or roles. It allows administrators or privileged users to control access to database objects such as tables, views, procedures, and functions.

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MySQL, as a relational database management system, supports various types of tables to store and organize data. Here are some commonly used table types in MySQL:

  • InnoDB
  • MyISAM
  • Memory
  • Archive
  • CSV
  • Partitioned
  • Federated
  • Blackhole
  • Merge

Answer:

In SQL, a live lock refers to a situation where multiple transactions are continuously attempting to acquire resources or locks on the database, but none of them can proceed because they are constantly being blocked by one another. Essentially, it is a special type of deadlock.

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We can use the SET ROWCOUNT command to limit the number of rows affected by a query to delete the duplicate records.

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ISAM stands for Indexed Sequential Access Method. It is a data access method used in computer systems and databases to store and retrieve data efficiently. ISAM combines the sequential access method, which reads data in a sequential order, with indexing techniques for faster data retrieval.

Answer:

Here are the different types of SQL sandboxes based on safety and access:

  • Safe Sandbox: A safe sandbox provides a controlled and restricted environment for executing SQL queries. Its key characteristics includes query restrictions, resource limitations, and data isolation.
  • Unsafe Sandbox: An unsafe sandbox provides fewer restrictions and safety measures compared to a safe sandbox. It is intended for advanced users who require more flexibility and control over their SQL environment. The characteristics of an unsafe sandbox include, full query access, limit data isolation, and resource usage.
  • External Access Sandbox: An external access sandbox extends the capabilities of a sandbox by allowing connections from external systems or applications. It enables users to access the sandboxed database from remote locations or integrate it with external tools. Some key features of an external access sandbox are remote connectivity, security measures, and integration possibilities.

Answer:

A right outer join is a type of join operation in relational databases that combines records from two tables based on a specified condition, including all the rows from the right table and only the matching rows from the left table. In other words, it returns all the rows from the right table and the matching rows from the left table, and for the non-matching rows in the left table, NULL values are used for the columns of the right table.

Answer:

Database black box testing in SQL refers to the process of testing a database without considering its internal structure or implementation details. It focuses on validating the functionality and behavior of the database by treating it as a “black box,” where only input and output are considered. It involves data mapping, data stored and retrieved with the Use of Black Box testing techniques like BVA and Equivalence Partitioning.

Answer:

To rename a column name in SQL Server, you can use the sp_rename system stored procedure. Firstly, you need to go to the table where the column is present and choose Design from the Object Explorer window pane. Now select the name you want to rename under the Column Name, and enter the new name. Thereby, navigate to the File menu and click Save.

Answer:

To connect to a SQL Server database, you can follow these steps:

  1. Install SQL Server: Ensure that SQL Server is installed on your machine or accessible on a remote server. If you don’t have SQL Server installed, you can download and install the appropriate version from the official Microsoft website.
  2. Obtain the necessary connection details: Gather the required information to establish a connection:
    • Server name or IP address: The name or IP address of the machine where SQL Server is installed.
    • Port number: The port on which SQL Server is listening (default is 1433).
    • Database name: The name of the specific database you want to connect to.
    • Authentication credentials: The username and password or integrated security details required to access the database.
  3. Choose a programming language or tool: Determine the programming language or tool you’ll use to connect to the SQL Server database. Popular options include:
    • C# (.NET Framework or .NET Core)
    • Java
    • Python
    • Node.js
    • PHP
    • SQL Server Management Studio (SSMS)
  4. Connect using your chosen programming language or tool: The specific code or steps may vary depending on the language or tool you’re using.
  5. Verify that your SQL Server is connected successfully: Expand and explore the objects within Object Explorer where the server’s name, username and SQL Server version are displayed.

Answer:

To find the server names in SQL Server, you can use one of the following methods:

  • SQL Server Management Studio (SSMS)
  • SQL Server Configuration Manager
  • PowerShell
  • SQLCMD Utility