SQL Server connection in Power BI - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding SQL Server Connection Strings in Power BI

Which of the following connection strings correctly connects Power BI to a SQL Server instance named SQLPROD01 on the default port, using Windows Authentication?

A Data Source=SQLPROD01;Initial Catalog=SalesDB;Integrated Security=False;

B Server=SQLPROD01,1433;Database=SalesDB;User Id=admin;Password=pass123;

C Server=SQLPROD01;Database=SalesDB;Integrated Security=False;User Id=admin;Password=pass123;

D Server=SQLPROD01;Database=SalesDB;Trusted_Connection=True;

💡 Hint

Windows Authentication uses Trusted_Connection=True or Integrated Security=True.

Option D uses Trusted_Connection=True, which enables Windows Authentication. It specifies the server and database correctly without specifying a port, which defaults to 1433.

❓ dax_lod_result

intermediate

DAX Measure for SQL Server Data Refresh Status

You have a table RefreshLog with columns RefreshDate and Status. You want a DAX measure that returns the count of successful refreshes in the last 7 days.

Which measure produces the correct result?

A SuccessfulRefreshes = COUNTROWS(FILTER(RefreshLog, RefreshLog[Status] = "Success" && RefreshLog[RefreshDate] <= TODAY() - 7))

B SuccessfulRefreshes = CALCULATE(COUNTROWS(RefreshLog), RefreshLog[Status] = "Success" && RefreshLog[RefreshDate] <= TODAY() + 7)

C SuccessfulRefreshes = CALCULATE(COUNTROWS(RefreshLog), FILTER(RefreshLog, RefreshLog[Status] = "Success" && RefreshLog[RefreshDate] >= TODAY() - 7))

D SuccessfulRefreshes = CALCULATE(COUNTROWS(RefreshLog), RefreshLog[Status] = "Success", RefreshLog[RefreshDate] >= TODAY() - 7)

💡 Hint

Use FILTER inside CALCULATE to apply multiple conditions correctly.

Option C correctly filters rows where Status is "Success" and RefreshDate is within the last 7 days (greater or equal to TODAY() - 7).

❓ visualization

advanced

Best Visualization for SQL Server Query Performance Over Time

You have imported SQL Server query performance data with columns QueryName, ExecutionTime (in milliseconds), and ExecutionDate. You want to visualize trends of execution time for multiple queries over the last month.

Which visualization type is best suited for this purpose in Power BI?

A Table showing <code>QueryName</code> and average <code>ExecutionTime</code> for the last month

B Line Chart with <code>ExecutionDate</code> on X-axis and <code>ExecutionTime</code> on Y-axis, with separate lines for each <code>QueryName</code>

C Pie Chart showing percentage of total execution time by query

D Stacked Bar Chart showing total execution time per query for the last month

💡 Hint

To show trends over time for multiple categories, use a line chart with series.

Option B allows you to see how execution time changes over dates for each query separately, making trends easy to spot.

🔧 Formula Fix

advanced

Troubleshooting SQL Server Connection Timeout in Power BI

You try to connect Power BI to a remote SQL Server but get a timeout error. Which of the following is the most likely cause?

A The SQL Server instance is not configured to allow remote connections.

B The Power BI desktop version is outdated and incompatible with SQL Server.

C The SQL Server database is empty with no tables.

D The Power BI report has too many visuals causing slow rendering.

💡 Hint

Timeout errors usually relate to network or server settings.

If SQL Server does not allow remote connections, Power BI cannot connect and will timeout. Other options do not cause connection timeout.

❓ data_modeling

expert

Optimizing Data Model for SQL Server DirectQuery in Power BI

You are using DirectQuery mode to connect Power BI to a large SQL Server database. To improve report performance, which modeling practice is best?

A Use star schema with fact and dimension tables, minimize calculated columns, and push calculations to SQL Server views.

B Import all tables fully and create many calculated columns in Power BI.

C Create many-to-many relationships between all tables to increase flexibility.

D Disable query folding to ensure all transformations happen in Power BI.

💡 Hint

Good data modeling and pushing calculations to the source improves DirectQuery performance.

Option A follows best practices: star schema simplifies queries, minimizing calculated columns reduces load, and pushing calculations to SQL Server leverages its power.

Practice

1. What is the main purpose of connecting Power BI to a SQL Server database?

easy

A. To import or query data directly for creating reports

B. To design the SQL Server database schema

C. To write SQL Server stored procedures

D. To backup the SQL Server database

Solution

1. Step 1: Understand Power BI data sources

   Power BI connects to data sources like SQL Server to get data for reports.

2. Step 2: Identify the purpose of connection

   The connection allows importing or querying data to visualize it in Power BI.

3. Final Answer:

   To import or query data directly for creating reports -> Option A

4. Quick Check:

   Power BI connection = data import/query [OK]

Hint: Power BI connects to get data, not to manage database [OK]

Common Mistakes:

• Confusing Power BI with database design tools
• Thinking connection is for database backup
• Assuming Power BI writes SQL code

2. Which of the following is the correct way to specify the server name when connecting Power BI to SQL Server?

easy

A. ServerName/InstanceName

B. ServerName\InstanceName

C. ServerName-InstanceName

D. ServerName.InstanceName

Solution

1. Step 1: Recall SQL Server instance naming

   SQL Server uses backslash \ to separate server and instance names.

2. Step 2: Match correct syntax

   The correct format is ServerName\InstanceName, not with slashes or dots.

3. Final Answer:

   ServerName\InstanceName -> Option B

4. Quick Check:

   SQL Server instance separator = \ [OK]

Hint: Use backslash \ between server and instance [OK]

Common Mistakes:

• Using forward slash or dot instead of backslash
• Omitting instance name when required
• Adding spaces around the backslash

3. You connect Power BI to SQL Server using DirectQuery mode. What happens when you refresh the report visuals?

medium

A. Power BI imports all data again from SQL Server

B. Power BI uses cached data and does not query SQL Server

C. Power BI queries the SQL Server live for updated data

D. Power BI disconnects from SQL Server after refresh

Solution

1. Step 1: Understand DirectQuery mode

   DirectQuery mode means Power BI sends live queries to the database on demand.

2. Step 2: Identify refresh behavior

   Refreshing visuals triggers live queries to SQL Server for current data.

3. Final Answer:

   Power BI queries the SQL Server live for updated data -> Option C

4. Quick Check:

   DirectQuery = live queries on refresh [OK]

Hint: DirectQuery means live data queries, not cached data [OK]

Common Mistakes:

• Confusing DirectQuery with Import mode
• Thinking refresh always imports all data
• Assuming Power BI disconnects after refresh

4. You try to connect Power BI to SQL Server but get an error: "Cannot connect to server." What is the most likely cause?

medium

A. Incorrect server or database name entered

B. Power BI does not support SQL Server connections

C. Your computer is offline but server is reachable

D. You forgot to install Power BI Desktop

Solution

1. Step 1: Check connection error meaning

   "Cannot connect to server" usually means wrong server or database info.

2. Step 2: Rule out other causes

   Power BI supports SQL Server; offline computer means no connection; Power BI Desktop must be installed.

3. Final Answer:

   Incorrect server or database name entered -> Option A

4. Quick Check:

   Connection error = wrong server/database name [OK]

Hint: Double-check server and database names for typos [OK]

Common Mistakes:

• Assuming Power BI lacks SQL Server support
• Ignoring network or firewall issues
• Not verifying Power BI installation

5. You want to create a Power BI report that always shows the latest sales data from SQL Server without importing all data each time. Which connection mode should you choose and why?

hard

A. DirectQuery, because it imports all data once

B. Import, because it loads all data once and never updates

C. Import, because it queries live data on demand

D. DirectQuery, because it queries live data on demand

Solution

1. Step 1: Understand Import vs DirectQuery

   Import loads data once; DirectQuery queries live data each time.

2. Step 2: Choose mode for latest data without full import

   DirectQuery fits because it fetches current data without importing all.

3. Final Answer:

   DirectQuery, because it queries live data on demand -> Option D

4. Quick Check:

   Latest data without import = DirectQuery [OK]

Hint: Use DirectQuery for live data, Import for snapshot [OK]

Common Mistakes:

• Confusing Import with live querying
• Choosing Import when data freshness is needed
• Misunderstanding DirectQuery behavior