Top 10 Power BI Interview Questions (based on what I usually ask)

Summary

In this video, the host discusses the top 10 Power BI interview questions through a fun spin-the-wheel format, offering valuable insights into key concepts such as measures vs. calculated columns, publishing reports, handling missing data, and DAX formulas. The video is interactive, encouraging viewers to engage by answering certain questions in the comments. The host also shares tips from personal experiences, making the advice practical and relatable. The video ends with an invitation to join a Power BI weekend workshop to further enhance skills and confidence.

Takeaways

• 📊 **Measure vs. Calculated Column**: A measure is used for calculations on top of a table, like counting rows, while a calculated column is part of the table, used for calculations within the table itself.
• 🔄 **Publishing Process**: To publish a Power BI report, save the file, then use the 'Publish' button in Power BI Desktop to upload it to the Power BI service, making it accessible to others in a selected workspace.
• 📉 **Handling Missing Data**: Strategies for dealing with missing data include ignoring non-essential values, requesting data from the source, or using imputation techniques like averaging.
• 💡 **DAX (Data Analysis Expressions)**: DAX is Power BI's calculation language used for creating measures, calculated columns, and tables. An example is counting shipments and filtering them by geography.
• 🔗 **Connecting Multiple Data Sources**: Power BI allows connecting to multiple data sources using Power Query, which can then be merged, appended, or combined to create a unified dataset.
• 💻 **Power BI Desktop vs. Service**: Desktop is for creating and designing reports, while the service is for publishing and sharing them with others.
• ⏱️ **Performance Optimization**: To improve report performance, reduce the amount of data loaded, remove unnecessary visuals, and use the performance profiler to identify and optimize slow elements.
• 🔐 **Row-Level Security (RLS)**: RLS in Power BI restricts data visibility based on user roles, ensuring that users only see relevant data.
• 🌀 **Slowly Changing Dimension (SCD)**: SCDs are dimensions that change over time but not frequently. They are managed by tracking changes in separate tables or rows with effective dates.
• 🎉 **Power BI Weekend**: An annual event where attendees can learn to use Power BI and gain confidence in using the software, with the next event scheduled for November 18th and 19th, 2023.

Q & A

What is the difference between a measure and a calculated column in Power BI?

A measure in Power BI is used to calculate things on top of a table, such as counting rows, while a calculated column is part of the table itself, used to calculate values within the table, like a discount rate based on order quantity.

How do you publish a Power BI report to the Power BI service?

After creating and testing a report in Power BI Desktop, you save the file and click the publish button. This publishes the report and dataset to an online workspace, making it accessible to anyone with access to that workspace.

How would you handle missing data in Power BI?

Handling missing data in Power BI can involve ignoring non-critical missing values, requesting the data from the source, or using imputation techniques like replacing missing values with the average or median of the column.

What is DAX and can you provide an example of a DAX formula you've used?

DAX stands for Data Analysis Expressions and is the calculation language in Power BI. An example of a DAX formula used is COUNTROWS for counting shipments in a table, which can then be sliced by geography to analyze shipments to different locations.

What steps would you take to connect multiple data sources to a Power BI report?

You can connect to multiple data sources in Power BI using Power Query. Once the data is imported, you can merge, append, or combine tables from different systems to create a composite table that can be loaded into Power BI.

What are the main differences between Power BI Desktop and Power BI Service?

Power BI Desktop is the tool used for creating and designing reports, while Power BI Service is used for publishing and sharing those reports with others within or outside the organization.

How do you optimize performance in Power BI reports?

To optimize performance, you can remove unnecessary data, reduce the number of visuals on a page, use the performance profiler to identify slow elements, and consider creating aggregate tables if appropriate.

What is RO level security in Power BI and how would you implement it?

Row level security (RO level security) in Power BI is used to restrict users from seeing certain data. It can be implemented by setting up security rules that define which users can access which data, often based on their role or other attributes.

What does the one star and the arrow mean in the data model diagram in Power BI?

In Power BI, a one-to-many relationship in the data model is indicated by a '1' and a star '*'. The arrow on the relationship line shows the direction of filter propagation, indicating which table's filters will affect the related table.

What is a slowly changing dimension (SCD) and how do you handle it in Power BI?

A slowly changing dimension is a type of dimension that changes over time but not frequently. In Power BI, you can handle SCD by tracking changes in a separate table or by maintaining historical rows with effective dates to analyze the impact of changes over time.

Outlines

00:00

📊 Power BI Interview Questions and Career Boost

The speaker introduces the topic of the video, which is about the top 10 Power BI interview questions aimed at helping viewers excel in job interviews and advance their careers in data analytics. A unique twist is added with the use of a spin wheel app to select questions in a random order, promising an ultimate surprise at the end of the video.

05:01

🔑 Understanding Measures vs. Calculated Columns in Power BI

The speaker explains the difference between a measure and a calculated column in Power BI. A measure is used to perform calculations on top of a table, such as counting rows, while a calculated column is part of the table itself, used for calculations like discount rates based on order quantity. The analogy of a hand is used to differentiate between the two, with measures being external to the data table (like gloves) and calculated columns being integral parts of the table (like fingers).

10:03

📈 Publishing Power BI Reports and Handling Missing Data

The process of publishing a Power BI report to the Power BI service is described, emphasizing the importance of testing before publishing to ensure accuracy and the accessibility of the report to authorized individuals within a workspace. The speaker also discusses strategies for handling missing data, such as ignoring non-critical missing values, requesting data from the source, or using imputation techniques like calculating the average of a column to fill in missing values.

15:03

💡 DAX in Power BI and Connecting Multiple Data Sources

DAX (Data Analysis Expressions) is introduced as the calculation language of Power BI, used for creating measures, calculated columns, and tables. The speaker shares a personal example of using DAX to count shipments and analyze low box shipments, and how it was visualized by geography and other dimensions. Additionally, the steps for connecting multiple data sources to a Power BI report are outlined, including using Power Query to merge, append, or combine data from different systems.

🛠️ Optimizing Power BI Report Performance

The speaker shares personal experience optimizing a Power BI report's performance by removing unnecessary data, such as historical data no longer needed for analysis. They also discuss the removal of non-essential visuals and graphical elements from report pages to reduce load times. The use of Power BI's built-in performance profiler to identify and address elements with high query and rendering times is mentioned as a strategy to improve report performance.

🔐 Implementing Row-Level Security in Power BI

Row-level security (RLS) in Power BI is briefly introduced as a feature to restrict data visibility based on user roles, such as allowing managers to see all data while limiting line employees to their relevant data. The speaker encourages viewers to share their experiences with implementing RLS in the comments section.

🌟 Understanding Data Model Relationships and Slowly Changing Dimensions

The speaker explains the symbols used in Power BI's data model diagram to represent relationships between tables, such as the one-to-many relationship indicated by '1' and '*'. The concept of slowly changing dimensions (SCD) is introduced, using the example of a product table where the cocoa percentage might change over time. The speaker suggests handling SCD by tracking changes in a separate table or by updating the values directly, depending on the significance of the change.

🎉 Power BI Weekend and Career Advancement

The speaker announces an upcoming Power BI weekend event on November 18th and 19th, 2023, designed to help attendees gain confidence and proficiency in using Power BI. The event includes a bonus Power BI cheat sheet for early registrants. The speaker concludes by wishing viewers success in their Power BI interviews and encourages them to explore other videos or sign up for the Power BI weekend.

Keywords

💡Power BI

Power BI is a business analytics service by Microsoft that enables users to visualize data, create reports, and gain business insights. In the video, Power BI is the central theme, with the speaker discussing various aspects of using Power BI for data analytics and preparing for job interviews in the field.

💡Measure

A measure in Power BI is a formula that performs calculations such as sums, counts, averages, and more on data that is aggregated from a table. The video explains measures as something that acts on top of a table but is not part of the table itself, using the example of counting shipments.

💡Calculated Column

A calculated column in Power BI is a new column created within a table that performs calculations based on existing columns. The video distinguishes calculated columns from measures by illustrating them as part of the table, likening them to fingers on a hand, in contrast to measures which are external to the table.

💡Publishing Reports

Publishing a Power BI report involves saving the report and data set and uploading them to the Power BI service, making them accessible to others in a selected workspace. The video emphasizes the importance of thorough testing before publishing to ensure accuracy and professionalism.

💡Missing Data

Handling missing data is a common challenge in data analysis. The video discusses strategies for dealing with missing data in Power BI, such as ignoring non-critical missing values, requesting data from the source, or using imputation techniques like averaging to fill in gaps.

💡DAX (Data Analysis Expressions)

DAX is the formula language used in Power BI for creating calculations, such as measures and calculated columns. The video provides an example of a DAX formula used to count shipments and another for counting low-box shipments, demonstrating its utility in data analysis.

💡Connecting Multiple Data Sources

Power BI allows users to connect to multiple data sources, which can then be combined and manipulated using Power Query. The video describes the process of adding new connections and merging data from different systems to create comprehensive reports.

💡Power BI Desktop vs. Power BI Service

Power BI Desktop is the tool used for creating and designing reports, while Power BI Service is for publishing and sharing those reports. The video clarifies that Desktop is for creation and Service is for consumption, highlighting the different roles of each tool in the data analytics process.

💡Performance Optimization

Performance optimization in Power BI reports involves techniques to improve the speed and efficiency of report loading and data processing. The video suggests strategies such as reducing data volume, removing unnecessary visuals, and using the performance profiler tool to identify and address bottlenecks.

💡RO (Row-level) Security

Row-level security in Power BI is a feature that restricts access to certain data rows based on the user's role or identity. The video uses the example of a manager versus a line employee to illustrate how RO security can be used to control the visibility of data within a report.

💡Slowly Changing Dimension (SCD)

A slowly changing dimension refers to data that changes infrequently over time but still requires tracking for historical analysis. The video gives the example of a product's cocoa percentage, which might change occasionally based on feedback. SCDs are important for maintaining historical data integrity in reports.

Highlights

Unlock your dream job in data analytics by mastering Power BI interview questions.

Learn the difference between a measure and a calculated column in Power BI.

A measure acts on top of a table, while a calculated column is part of the table itself.

Discover the process of publishing a Power BI report to the Power BI service.

Ensure reports are thoroughly tested before publishing to avoid mistakes.

Handle missing data in Power BI by ignoring, requesting, or imputing values.

DAX (Data Analysis Expressions) is the calculation language of Power BI.

Use DAX to create measures, calculate columns, and even entire tables.

Connect multiple data sources to a Power BI report using Power Query.

Merge, append, or combine tables from different systems for a comprehensive data model.

Understand the main differences between Power BI Desktop and Power BI Service.

Optimize performance in Power BI reports by reducing data points and removing unnecessary visuals.

Use the performance profiler in Power BI to identify and improve slow-rendering elements.

Learn about RO (Row-level) security in Power BI to restrict data visibility.

Implement RO level security based on user roles to control data access.

Understand the symbols in the data model diagram, such as '1' and '*' for relationships.

The arrow in data model diagrams indicates the direction of filter propagation.

Explore the concept of Slowly Changing Dimension (SCD) in Power BI.

Manage SCD by tracking changes over time, such as product attributes.

Join the Power BI weekend event on November 18th and 19th, 2023, to boost your skills.

Get a Power BI cheat sheet bonus when you sign up for the Power BI weekend event.

Transcripts

are you ready to unlock your dream job

in the world of data analytics and boost

your earnings potential well you have

come to the right place in today's video

I'm going to talk about the top 10

powerbi interview questions so that you

can transform your career but there is a

Twist a literal twist I got here a spin

wheel app and I'm going to spin this and

take up these questions in the random

order you don't want to miss the ending

for an ultimate surprise so let's go for

a spin okay so the first one is going to

be number

two can you explain the difference

between a measure and a calculated

column now a measure is something that

we can use to calculate things on top of

a table so for example if I have got

some shipment data in a table and I just

want to count how many shipments are

there we can use a measure like count

rows on top of the shipments table to

count the number of shipments whereas a

calculated column is something that is

part of the table so in the shipments

table we can use a calculated column to

calculate the discount rate based on the

order quantity of that

shipment one simple way to think about

about these is if you think your data

table as this hand then a measure is

something that is outside this hand so

it acts on top of the hand but it's not

part of the hand whereas a calculated

column is like one of the fingers in

your hand it is part of the hand itself

so that is the main difference between

these two things this is a lot harder

than I

imagined

[Music]

so the next one is question number seven

describe the process of publishing a

powerbi report to the powerbi

service so the process begins like this

once you finished creating the report

and testing it and sure that you're

happy with the results then you save the

file and you hit the publish button in

the powerbi desktop this is going to

take your report as well as the data set

and then publish it to online platform

in a workspace that you select from that

point onwards your report is available

for anybody who has access to that

workspace so this is why it is important

to properly test your reports before you

publish them because once it is out

anyone in your organization who can get

to that workspace can see what you have

created so you don't want to have any

mistakes the process also involves

selecting the the workspace and making

sure that the right people have access

to that workspace that sort of a thing

can be set up in the powerbi service

Itself by either you or your it

[Music]

administrator the next one is number

10 how would you handle missing data in

powerbi so when you get questions like

this it's a good idea to not just give

textbook style answers it is also

important and probably more valuable if

you give answers from your own previous

experiences either in work or life so

I'm going to give you an example from

when I had to deal with missing data

recently in a powerbi project we were

looking at data that is collected from

external parties now we sent out a

survey asking external parties to fill

out the survey and then we are analyzing

it naturally as we don't have control

over this data there were many missing

values and the strategy that we used is

multifold for certain missing values as

they're not too important for our

analysis we choose to ignore them so we

didn't bother analyzing or considering

those averages or values when

calculating

summaries for other kinds of missing

data we choose to again go back to the

source and ask them again if they can

provide these missing values so that is

another strategy that I would use the

third option is something that I also

used because certain missing values we

couldn't go back and ask them so this is

where I used a technique called

imputation so let's say we have got some

values and there is one missing value in

the middle somewhere we can impute that

missing value by for example calculating

the average of the overall column

excluding those missing values and then

using that average as the missing value

we could also use median mode or any

other statistical metric there power

query which is the main place where your

data comes into powerbi offers many ways

to handle these missing values it also

helpfully identifies if there is a

missing value in your

data and the next one

is question number five

what is Dax and can you give me an

example of a recent Dax formula you have

used Dax stands for data analysis

Expressions it is the main calculation

language of powerbi using tax we can

calculate measures we can calculate

columns we can even calculate tables as

part of the

powerbi a recent example that I used is

similar to what I mentioned earlier the

shipment count measure so we have got a

shipments table and I wanted to know how

many shipments are done so I used a

count Rose measure on the shipments

table to count how many shipments are

there and then I took this measure and

sliced it by geography so that I can see

how many shipments are going to India or

New Zealand or Australia some of the

geographies in which my previous company

operated a more advanced version of the

same shipment count measure is low box

shipment count this is where sometimes

we send shipments with very few boxes of

chocolate in them did I mention I used

to work in a chocolate company so I

wanted to count how many times we are

shipping where the Box count is less

than 50 so I used a Dax formula on

shipment count along with calculate

formula to introduce an extra filter to

calculate how many low box shipments are

there and then I again was able to

visualize this by product or by

salesperson to understand who is sending

more low boox shipments while I'm going

to keep my finger busy by tapping this

pin button I want you to keep your

finger busy by tapping that like button

if you're enjoying this video so go

ahead and do

that the next one is number three

describe the steps you would take to

connect multiple sources to a powerbi

report

when you open powerbi and when you're

trying to connect initially you can

bring in one data source this could be a

SQL Server table or an Excel file or a

web page but once you already have that

data in powerbi through Power query you

can add any number of connections so we

simply use par query and then make a new

connection once all the data is there

from different systems I can then use

power query to either merge the tables

or append them or combine the tables to

create a third composite table and load

that into

powerbi the next one is number

one what are the main differences

between powerbi desktop and powerbi

service powerbi desktop is the main

software or tool that I use as a data

analyst to create the reports or

calculate things or establish

connections and clean my data once I

finish my job I then use powerbi service

to publish and share the reports with

other people in my organization or

outside the organization so the key

difference between these two things is

one is a creation tool the desktop

application is the creation tool and the

service is the publishing tool so

consumption tool anybody who is usually

on the service their main intention is

going to be consume the data or reports

that you have published understand what

is going on and then take actions all

right we are at the last four now let's

see what this one brings

up number six how do you optimize the

performance in powerbi reports again I

want to remind you that when you get

questions like this instead of giving

theoretical or you know researched

answers give it from your experience

like what you did when you saw that a

report was slow so for example a recent

report that I built for a client was all

right initially but it was kind of

getting slow over a period of time so

here is what we did I first looked at

the data that is being used in the

report and I realized that even though

we are only analyzing 2023 performance

for some reason we are bringing data

from 2021 and 2022 as well initially

when when the report was created there

was a need to have those but the client

is no longer looking at those parts or

they are no longer interested in those

strengths so a simple thing that I did

is to remove all the 2021 and 2022 data

by updating the query part uh you could

do this in either power query or in our

case we actually modified the we

condition in the SQL so that the data

never came into Power query itself this

drastically reduced the amount of data

points that are coming into powerp and

improveed the

performance but let's just say that

could not fix the problem you you still

had to see all of this data then the

next things that I would do is I would

look at the page where the data is being

presented and then I will ask questions

about are there any unnecessary visuals

or graphical elements that are not

contributing to the overall analysis if

so I would take them out because every

little thing on the page is going to add

a little bit of load time to the report

even if that could not solve the problem

then I will use a performance profiler

our bi has a built-in profiler option so

that I can run it and then measure for

each of the elements on the page how

much time they're taking both for query

as well as rendering and then I will try

to attack the items that have very high

render values a simple technique

although I've never used it previously

is rather than loading the raw data you

could also consider building some

aggregate tables powerbi offers native

way to do this I never done did that as

there was no requirement for that but

that option is also available okay only

three

more number

eight now for this one I'm not going to

answer the question simply because I I

do know the answer it's just that I

thought it'll be fun if you also get a

chance to answer this question so I'll

read out the question I'll give you a

short answer but I want you to answer

this in the comments below explain the

RO level security in powerp how would

you implement it so Ro level security is

a feature of powerbi that we can use to

restrict people from

seeing parts of the data that they

shouldn't be seeing so for example if

you are a manager you can see everything

but if you are a line employe

you should only be seeing information

that pertains to you so you can use Ro

level security to do that now how would

you answer this again use your life

experiences either from work or personal

projects that you have done and tell me

in the comments how you would answer

this interview

question okay only two

more number

four and that makes number six as the

last one or I think number nine as the

last one

yeah

uh what does the one star and the arrow

mean in the data model

diagram So within powerbi when you have

multiple tables you can create a data

model in the data model will have these

extra symbols between the tables on the

line that connects them so a one and

star means the relationship is one to

many a simple example is going back to

the shipment table that I was talking

about

in each shipment we will have a product

code and a corresponding product

Dimension table that tells us more about

these products so the relationship

between shipments and products table is

many to one that means many shipments

can be for the same product so the many

side is usually denoted with star and

one side is denoted with one and then

there is also an arrow usually pointing

from product table to the shipments

table what this arrow means is the

filters will flow from product table

down to the shipments table so that

Arrow indicates the propagation of

filters uh a simple way to think about

this is in a report if I have got a

slicer on a product category and I

select a specific category like bars in

the product category slicer then because

that slicer is in the product table my

product table is going to be filtered

first and as the arrow say is the filter

should now propagate down to shipments

it's going to come down to shipments

table shrink the shipment table to just

the selected categories records and then

all the values on the screen will be

calculated for that so that's what these

symbols mean and now the last question

is number nine which is what is a slowly

changing Dimension SCD give me an

example and how you handle it so again

I'm going to partly answer this but I

want you to think about it and use the

comments to write your experience with

SCD a slowly changing Dimension is any

Dimension that slowly changes over time

so a simple example is going back to the

previous one my product table within the

product table we have a option called

Coco percentage so we sell chocolate so

every product has a certain percent of

cocoa in it and that percent is usually

fix it for many of our products but some

of the more experimental products we

might tweak this over a period of time

so initially a product might have 20%

Coco but based on the customer feedback

we might choose to reduce it down to 18%

or increase it to

30% so that that column itself is it's

not changing every day but it changes

maybe once every 6 months or once a year

depending on seasonal patterns and

whatnot now when that happens

that is a slowly changing Dimension

because that aspect of that Dimension is

changing

slowly uh and you can handle this by

keeping track of the percentages in

another separate table or having

separate rows every time such change

happened with an effective date uh let's

say you wanted to understand what impact

that cocoa percentage had on customer

satisfaction or shipment count or

something else uh you you need to know

what was the percentage before and after

that slow change happened so we need to

have those records in some other cases

if it is a trivial thing we wouldn't

bother keeping all the values we just

update delete the old value and put the

new value so that is an example of a

slow changing

Dimension how do you answer this again

put your choices or options in the

comments now let's talk about the

surprise if you are thinking all of

these questions are fine but I don't

understand

that well enough I don't have that

technical understanding or the

confidence then I have got good news for

you I'm running my annual powerbi

weekend this year on November 18th and

19th in this powerbi weekend it's a 4our

event so 2 hours on Saturday 2 hours on

Sunday we are going to meet in an online

meeting and I will be teaching how to

use powerbi so that you can gain that

initial confidence and comfort level

around this software it's happening on

November 18th and 19th in 2023 but if

you're watching this after that date you

can still find the next iteration of

this event details in the video

description below so the tickets for

this are on sale go ahead and sign up

now if you sign up now you will get a

powerbi cheat sheet as an extra bonus as

well so go ahead and check that out

powerbi weekend happening on November 18

and 19 now whether you choose to attend

this powerbi weekend or not I sincerely

wish you all the very best with your

upcoming powerbi interview I hope you

will get that job thank you so much for

watching and check out some of my other

videos that show up on the screen or

sign up for the powerbi weend

bye-bye