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Power BI Questions and Answers > Clean, transform, and load data in Power BI > Flashcards

Clean, transform, and load data in Power BI Flashcards

1
Q

Why is data cleaning important in Power BI?

A

To ensure the accuracy and reliability of data, making it ready for analysis and reporting.

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2
Q

What is the first step in the data cleaning process in Power BI?

A

Profiling the data to understand its structure and quality.

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3
Q

What tool is commonly used for data cleaning in Power BI?

A

Power Query Editor.

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4
Q

What are some common data cleaning tasks in Power BI?

A

Removing duplicates, handling missing values, and correcting data types.

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5
Q

What is the primary purpose of shaping data in Power BI?

A

To transform and refine raw data into a structured format suitable for analysis.

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6
Q

What are some common data shaping tasks in Power BI?

A

Filtering rows, removing columns, grouping data, and creating calculated columns.

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7
Q

Which tool in Power BI is used for shaping data?

A

Power Query Editor.

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8
Q

How can you ensure data quality during the shaping process?

A

By performing data validation checks and applying consistent data transformation rules.

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9
Q

What is the process of grouping data in Power BI?

A

Grouping data involves aggregating data based on specific criteria to summarize and analyze it more effectively.

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10
Q

How can you pivot data in Power BI?

A

Use the “Pivot Column” feature in Power Query Editor to transform rows into columns based on a key field.

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11
Q

What is the role of the “Unpivot Columns” feature?

A

It transforms columns into rows, making it easier to analyze data that was previously spread across multiple columns.

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12
Q

What is a calculated column in Power BI?

A

A column created using DAX expressions to perform calculations on existing data within the model.

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13
Q

Why might you want to rename queries in Power BI?

A

To make query names more obvious and user-friendly, improving clarity and usability.

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14
Q

How can you replace null values in Power Query Editor?

A

By selecting the column, clicking Replace Values, entering null in the Value to Find box, and the replacement value (e.g., zero).

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15
Q

Why is it important to remove duplicate values from columns in Power BI?

A

To ensure data accuracy and uniqueness, which can improve data analysis and reporting.

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16
Q

Why is setting the correct data type important in Power BI?

A

Ensures data accuracy and optimizes performance in calculations and visualizations.

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17
Q

What are common data types you might set in Power BI?

A

Text, Date, Whole Number, Decimal Number, and Boolean.

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18
Q

How can data type mismatches affect Power BI reports?

A

They can lead to errors in calculations, incorrect aggregations, and issues in data visualizations.

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19
Q

Why would you want to combine tables in Power BI?

A

To simplify the model by reducing the number of tables, handle tables with similar roles, merge tables with few columns into another, or use columns from different tables in a custom column.

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20
Q

What are the two methods to combine tables in Power BI?

A

Merging and appending.

21
Q

What is appending queries in Power BI?

A

Adding rows from one table to another, resulting in a combined table with more rows.

22
Q

How do you append queries in Power BI?

A

Use the “Append Queries” option in Power Query Editor, selecting either “Append Queries” or “Append Queries as New” to create a new table.

23
Q

What must be consistent when appending tables in Power BI?

A

The column headers and data types should be the same across all tables being appended.

24
Q

What is merging queries in Power BI?

A

Combining columns from multiple tables into one based on a common column, similar to SQL JOIN operations.

25
Q

What is a key requirement for merging tables?

A

A common column, or key, that exists in both tables to align the data correctly.

26
Q

What are the join types available in Power BI when merging tables?

A

Left Outer, Full Outer, and Inner joins.

27
Q

Describe a Left Outer join in Power BI.

A

It displays all rows from the first table and only the matching rows from the second table.

28
Q

Describe a Full Outer join in Power BI.

A

It displays all rows from both tables, combining data where possible.

29
Q

Describe an Inner join in Power BI.

A

It displays only the rows that have matching values in both tables.

30
Q

What should you do before combining tables in Power BI?

A

Remove any unnecessary columns to streamline the resulting combined table.

31
Q

What is the purpose of profiling data in Power BI?

A

To study the nuances of data, determine anomalies, examine underlying data structures, and query data statistics like row counts and value distributions.

32
Q

What should you do before examining data in Power Query Editor?

A

Learn about the underlying data structures, viewable under the Model tab in Power BI Desktop.

33
Q

What can you do under the Model tab in Power BI Desktop?

A

Edit column and table properties, transform data using the Transform Data button, and manage relationships between tables.

34
Q

What feature in Power Query Editor helps identify data anomalies?

A

The Column Distribution feature under the View tab in the ribbon.

35
Q

What does the Column Quality feature show?

A

Percentages of data that is valid, in error, and empty.

36
Q

What is the significance of Column Distribution in Power Query Editor?

A

It shows the distribution of data within a column and the counts of distinct and unique values.

37
Q

What detailed statistics does the Column Profile provide?

A

Row counts, outliers, empty rows, minimum and maximum values, and value distribution.

38
Q

How can you change the default behavior of profiling only the first 1000 rows?

A

Select the profiling status in the status bar and choose “Column profiling based on entire data set.”

39
Q

What additional statistics are provided for numeric columns in Column Statistics?

A

Count of zeroes, null values, average value, standard deviation, and counts of even and odd values.

40
Q

What is the purpose of the Advanced Editor in Power BI?

A

To view and directly modify the M code that Power Query uses to shape data.

41
Q

How do you access the Advanced Editor in Power Query?

A

By selecting the View ribbon and then clicking on Advanced Editor.

42
Q

What does each step in Power Query roughly correspond to in the Advanced Editor?

A

Each step corresponds to one or two lines of M code.

43
Q

Is it necessary to write M code to use Power Query?

A

No, it is not required, as most steps can be created using the graphical interface.

44
Q

How is M code written and structured?

A

M code is written top-down, where later steps can refer to previous steps by the variable name to the left of the equal sign.

45
Q

What should you be careful about when reordering steps in M code?

A

Reordering steps can ruin the statement dependencies, which can break the data transformation process.

46
Q

What is the ‘in’ statement used for in M code?

A

It is used to define the final data set result, typically referring to the last query step.

47
Q

How can the Advanced Editor be useful for customization?

A

It allows for modifications such as changing the name of a database directly in the code.

48
Q

What should you understand about each Power Query step created via the UI?

A

Each step is converted into M code, which can be read and modified in the Advanced Editor.

Power BI Questions and Answers (13 decks)

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