This post is a part of the PL-300: Microsoft Power BI Data Analyst Exam Prep Hub; and this topic falls under these sections:
Prepare the data (25–30%)
   --> Transform and load the data
      --> Merge and append queries

Below are 10 practice questions (with answers and explanations) for this topic of the exam.
There are also 2 practice tests for the PL-300 exam with 60 questions each (with answers) available on the hub.

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Practice Questions

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Question 1

You receive three Excel files containing sales data for Q1, Q2, and Q3. Each file has identical columns. You want to analyze total sales for the year. What is the BEST approach?

A. Merge the queries using an inner join
B. Merge the queries using a left outer join
C. Append the queries
D. Create relationships between the tables

✅ Correct Answer: C

Explanation:
Appending stacks rows from tables with the same structure. Since the quarterly files have identical columns, Append is the correct transformation. Merge is used for combining columns, not rows.

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Question 2

You have a Sales table with ProductID and a Products table with ProductID and ProductName. You want to add product names to the Sales table. Which transformation should you use?

A. Append queries
B. Merge queries with a left outer join
C. Merge queries with a full outer join
D. Create a calculated column

✅ Correct Answer: B

Explanation:
This is a classic lookup scenario. A left outer merge keeps all sales rows while adding matching product details.

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Question 3

What is the primary difference between Merge and Append in Power Query?

A. Merge works only with SQL sources
B. Append combines columns; merge combines rows
C. Merge combines rows; append combines columns
D. Merge combines columns; append combines rows

✅ Correct Answer: D

Explanation:
Merge combines tables side-by-side (columns) based on keys, while append stacks tables top-to-bottom (rows).

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Question 4

You append two tables with similar but not identical column names. What happens?

A. Power Query fails with an error
B. Columns are automatically renamed
C. New columns are created with null values where data doesn’t exist
D. Only matching columns are appended

✅ Correct Answer: C

Explanation:
When appending, Power Query keeps all columns and fills missing values with nulls, which can create sparse tables if structures don’t align.

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Question 5

Which join type returns only rows that do NOT have matching values between two tables?

A. Inner join
B. Left outer join
C. Anti join
D. Full outer join

✅ Correct Answer: C

Explanation:
Anti joins return non-matching rows and are often used for data validation and quality checks — a subtle but testable concept in PL-300.

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Question 6

A merge operation produces duplicate rows unexpectedly. What is the MOST likely cause?

A. Append was used instead of merge
B. The join key is not unique
C. The data types are mismatched
D. The wrong join type was selected

✅ Correct Answer: B

Explanation:
If the join key appears multiple times in either table, a merge can create many-to-many matches, resulting in duplicated rows.

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Question 7

Where should merge and append operations typically be performed for best model performance?

A. In DAX measures
B. In Power BI visuals
C. In the Power Query Editor
D. In calculated tables

✅ Correct Answer: C

Explanation:
Merge and append are data transformation tasks and should be done in Power Query before loading data into the model.

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Question 8

You want to combine historical and current transaction tables that represent the same data structure. What should you do FIRST?

A. Merge the tables
B. Append the tables
C. Create a relationship
D. Create a calculated column

✅ Correct Answer: B

Explanation:
Historical and current tables with the same structure should be appended to form a single fact table before modeling.

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Question 9

After merging two queries, the related table appears as a column with the word “Table” in each row. What must you do next?

A. Change the column data type
B. Expand the merged column
C. Rename the column
D. Create a relationship

✅ Correct Answer: B

Explanation:
After a merge, you must expand the nested table to select the columns you want to bring into the main query.

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Question 10

Which scenario BEST indicates that append should NOT be used?

A. Combining monthly sales files
B. Combining yearly budget tables
C. Adding customer details to a sales table
D. Combining regional sales data

✅ Correct Answer: C

Explanation:
Appending is for stacking similar datasets. Adding customer details requires merge, not append. This aligns with the PL-300 best practice: know when not to append.

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Key PL-300 Takeaways

• Append = same structure, more rows
• Merge = related tables, more columns
• Left outer join is the most common merge type
• Always validate keys and data types
• Do transformations in Power Query, not DAX

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