Power BI and SQL Interview Process

Introduction

Preparing for a Power BI and SQL interview requires more than technical knowledge. Interviewers typically assess your understanding of Power BI, SQL, data modeling, DAX, Power Query, report development, and your ability to solve real business problems. They also evaluate how effectively you communicate your project experience and approach technical challenges. This guide explains the common interview rounds, frequently asked questions, and practical tips to help you prepare with confidence.

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Round 1: Introduction and Background

The first round of the interview process is a 30-minute call where the candidate introduces themselves and shares their background. The interviewer discusses the job description, which is to hire a Power BI developer who can build reports, handle requirements, and publish reports to end users. The candidate should highlight their experience with BI tools, domains worked in, and primary and secondary skill sets. In this example, the candidate, Aruna, has 5+ years of experience working with PowerBI, with expertise in Finance, Telecom, and Retail domains.

Round 2: Project Experience and Technical Skills

In the second round, the candidate’s project experience and technical skills are assessed. The interviewer asks about the candidate’s project, the problem statement, and how their report helped the client. Aruna explains that her project involved building a retail sales analysis dashboard, providing insights into sales revenue and order trends. She gathered data from various sources like Excel, CSV, and SQL Server, and published the reports to end users through the Power BI app. Aruna also explains her involvement in the end-to-end process, including data gathering, ETL using Azure Data Factory (ADF), and report creation using Power BI.

Round 3: Power BI Service and SQL Skills

In the final round, the candidate’s knowledge of PowerBI Service and SQL is assessed. The interviewer asks about Aruna’s experience with PowerBI Service, including publishing reports, creating dashboards, setting up data gateways, and scheduling refreshes. Aruna explains that she schedules data refreshes every 15 days using Azure Data Factory (ADF) and PowerBI Service. She also mentions the recent updates she has observed in Power BI, such as new calculations, folder options, and DAX queries. Moving on to SQL, Aruna rates her SQL skills as 5 out of 10 and explains that she uses SQL for data validation, ad hoc requests, and comparing sales data.

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Row-Level Security and Object-Level Security

The interviewer asks Aruna about her experience with row-level security (RLS) and object-level security (OLS). Aruna mentions that she has implemented RLS to restrict access to certain data based on user roles. When asked about OLS, Aruna explains that she has implemented object-level security to restrict access to specific columns or schemas in the database. She also mentions using Table Editor in Power BI Desktop for implementing object-level security.

Challenges Faced and Problem-Solving Skills

Aruna discusses the technical challenges she faced in her project, such as keeping measure values as options in slicers and handling changing requirements. She explains how she overcame these challenges by creating individual measures and using DAX functions like HASONEVALUE and SELECTEDVALUE. Aruna also shares her experience of handling a reduced team size and managing changing requirements, which required extended timelines and flexibility. She highlights the importance of effective communication and problem-solving skills in overcoming these challenges.

Power BI Service and Data Refresh

The interviewer asks Aruna about data refresh in PowerBI Service. Aruna explains that she uses scheduled refresh to update the data every 15 days. She mentions installing data gateways, connecting to data sources like Excel and SQL Server, and setting up scheduled refresh in PowerBI Service. Aruna also clarifies that gateways are installed on the server and not directly in PowerBI Service.

Object-Level Security and Recent Updates

Aruna explains the need for object-level security and mentions that it is currently not possible in Power BI without using Table Editor. She also mentions that she keeps herself updated with the latest updates in PowerBI, such as new calculations, folder options, and DAX queries. However, she prefers using established features like Azure Data Factory and SQL for data processing and validation.

SQL Skills and Window Functions

Switching to SQL, the interviewer asks Aruna about her experience and skills. Aruna rates herself 5 out of 10 in SQL and mentions using SQL for data validation and ad hoc requests. When asked about window functions, Aruna mentions using aggregate functions like SUM, AVG, MIN, and MAX, as well as window functions like RANK, DENSE_RANK, and ROW_NUMBER. The interviewer asks Aruna to differentiate between aggregate functions and window functions. Aruna explains that aggregate functions work at the column level and include functions like SUM and AVG, while window functions work at the row level and include functions like RANK and ROW_NUMBER.

Interview Feedback and Areas for Power BI Improvement

The interviewer provides feedback to Aruna, stating that she needs to work on her confidence and clarity in expressing her answers. The interviewer suggests focusing on the basics, improving technical vocabulary, and practicing answering interview questions with more confidence. The interviewer also points out specific mistakes, such as not knowing where to install data gateways and not differentiating between scalar functions, aggregate functions, and window functions. Overall, the interviewer rates Aruna’s performance at 6 out of 10 and encourages her to continue practicing and improving.

Conclusion

A successful Power BI and SQL interview combines strong technical knowledge with practical project experience and clear communication. By mastering SQL fundamentals, Power BI concepts, DAX, data modeling, and real-world problem-solving, you can confidently handle technical discussions and demonstrate your ability to deliver business insights. Consistent practice and hands-on experience are the keys to interview success.

Frequently Asked Questions