Data source and dataset in Power BI - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding Data Sources in Power BI

Which of the following best describes a data source in Power BI?

A A location or service where raw data is stored and accessed by Power BI.

B A calculated column added to a dataset.

C A filter applied to data to show specific results.

D A visual report created from data in Power BI.

💡 Hint

Think about where Power BI gets its data from before processing.

A data source is where Power BI connects to get raw data, such as databases, files, or online services.

❓ data_output

intermediate

Dataset Content After Import

After importing data from an Excel file into Power BI, what does the dataset contain?

A The raw Excel file stored inside Power BI.

B Only the connection details to the Excel file without any data.

C A set of visual charts created automatically from the Excel data.

D The imported tables and their data ready for analysis and visualization.

💡 Hint

Consider what Power BI uses to build reports after importing.

The dataset contains the actual data tables imported from the source, which can be used to create visuals.

🔧 Formula Fix

advanced

Identifying the Error in Data Refresh

Power BI fails to refresh data from a SQL Server data source. Which option shows the most likely cause?

A The Power BI desktop version is outdated but data refresh always works offline.

B The SQL Server credentials used in Power BI are incorrect or expired.

C The dataset was created from an Excel file, not SQL Server.

D The Power BI report has too many visuals on one page.

💡 Hint

Think about what is needed to access data from a database during refresh.

Incorrect or expired credentials prevent Power BI from connecting to the SQL Server to refresh data.

🎯 Scenario

advanced

Choosing the Right Data Source for Real-Time Data

You need to build a Power BI report that shows real-time sales data updating every minute. Which data source type is best?

A A streaming dataset connected to a live API providing sales data.

B An Excel file uploaded manually once a day.

C A static CSV file stored on a local computer.

D A PowerPoint file with sales charts.

💡 Hint

Real-time means data updates automatically and frequently.

Streaming datasets connected to live APIs allow Power BI to update visuals in real time.

📊 Formula Result

expert

Power Query M Code Output for Dataset Preview

Given this Power Query M code snippet that loads data from a CSV file, what will be the output of Table.RowCount(Source) if the CSV has 100 rows?

let
  Source = Csv.Document(File.Contents("sales.csv"),[Delimiter=",", Columns=5, Encoding=1252, QuoteStyle=QuoteStyle.None])
in
  Table.RowCount(Source)

A 100

B 0

C Error: Table.RowCount expects a table but got a list

D 101

💡 Hint

Consider the type returned by Csv.Document and what Table.RowCount expects.

Csv.Document returns a list of lists, not a table, so Table.RowCount raises an error.

Practice

1. What is a data source in Power BI?

easy

A. The original location where data is stored before importing

B. A visual report created in Power BI

C. A chart made from data

D. A filter applied to data

Solution

1. Step 1: Understand the term 'data source'

   A data source is where data originally exists, like a database or file.

2. Step 2: Differentiate from dataset

   A dataset is the data imported into Power BI for analysis, not the original location.

3. Final Answer:

   The original location where data is stored before importing -> Option A

4. Quick Check:

   Data source = original data location [OK]

Hint: Data source is where data lives before Power BI imports it [OK]

Common Mistakes:

• Confusing data source with dataset
• Thinking data source is a report or visualization
• Mixing data source with filters

2. Which of the following is the correct way to add a new dataset in Power BI?

easy

A. Click 'Get Data' and select the data source to load data

B. Create a new report without connecting to any data

C. Use the 'Format' pane to add data

D. Right-click on a visual and select 'Add Dataset'

Solution

1. Step 1: Identify how to load data

   Power BI uses 'Get Data' to connect to data sources and load datasets.

2. Step 2: Eliminate incorrect options

   Creating reports without data or using format pane does not add datasets.

3. Final Answer:

   Click 'Get Data' and select the data source to load data -> Option A

4. Quick Check:

   Loading data = Get Data button [OK]

Hint: Use 'Get Data' to import datasets from sources [OK]

Common Mistakes:

• Trying to add data from the Format pane
• Assuming reports create datasets automatically
• Looking for dataset options in visuals

3. Consider this Power BI M code snippet to load data from a CSV file:

let
  Source = Csv.Document(File.Contents("C:\\Data\\sales.csv"),[Delimiter=",", Columns=3, Encoding=1252, QuoteStyle=QuoteStyle.None]),
  ChangedType = Table.TransformColumnTypes(Source,{{"Date", type date}, {"Sales", Int64.Type}, {"Region", type text}})
in
  ChangedType

What does the Source step represent?

medium

A. A visualization of sales data

B. The dataset after changing column types

C. The original data loaded from the CSV file

D. A filter applied to the sales data

Solution

1. Step 1: Analyze the 'Source' step

   'Source' uses Csv.Document and File.Contents to load raw data from the CSV file.

2. Step 2: Understand subsequent steps

   'ChangedType' modifies data types; 'Source' is before this, so raw data.

3. Final Answer:

   The original data loaded from the CSV file -> Option C

4. Quick Check:

   Source = raw data load step [OK]

Hint: 'Source' usually means raw data load in Power Query [OK]

Common Mistakes:

• Confusing 'Source' with transformed data
• Thinking 'Source' is a visualization
• Assuming 'Source' applies filters

4. You tried to load data from an Excel file in Power BI but got an error. Which of these is the most likely cause?

medium

A. You need to format the data as a table in Power BI

B. You forgot to create a report before loading data

C. Power BI does not support Excel files

D. The file path is incorrect or file is missing

Solution

1. Step 1: Identify common errors loading Excel data

   Incorrect file path or missing file causes load errors.

2. Step 2: Eliminate incorrect reasons

   Power BI supports Excel files; reports are created after loading data; formatting in Power BI is not required to load.

3. Final Answer:

   The file path is incorrect or file is missing -> Option D

4. Quick Check:

   File path errors cause load failures [OK]

Hint: Check file path first if data load fails [OK]

Common Mistakes:

• Thinking Power BI can't load Excel files
• Assuming report creation is needed before data load
• Believing data must be pre-formatted in Power BI

5. You want to combine sales data from two different Excel files into one dataset in Power BI. What is the best approach?

hard

A. Load both files as separate datasets and create a relationship between them

B. Use Power Query to append the two tables into a single dataset

C. Load one file and manually copy data from the other into Power BI

D. Create two reports, one for each file, and merge reports later

Solution

1. Step 1: Understand combining data sources

   Appending tables in Power Query merges data into one dataset for analysis.

2. Step 2: Evaluate other options

   Creating relationships keeps data separate; manual copying is inefficient; merging reports is not practical.

3. Final Answer:

   Use Power Query to append the two tables into a single dataset -> Option B

4. Quick Check:

   Append tables in Power Query to combine datasets [OK]

Hint: Append tables in Power Query to merge datasets [OK]

Common Mistakes:

• Using relationships instead of appending for combined data
• Copy-pasting data manually
• Merging reports instead of datasets