WGU D204 — The Data Professional: 250 Exam
Practice Questions (Data Analytics, SQL, Data
Management & Professional Practice)
These cover SQL fundamentals, data modeling, ETL/warehousing, data quality & governance,
machine learning, statistics, data visualization, privacy/security, NoSQL, big data, and
professional practice — aligned with the D204 course objectives. Good luck on your assessment
1. Which of the following best describes the role of a data analyst?
A) Designing hardware infrastructure for data storage B) Collecting, cleaning, and interpreting
data to support business decisions C) Writing operating system code for database servers D)
Managing network security for cloud platforms
B) Collecting, cleaning, and interpreting data to support business decisions (correct
answer)
Rationale: A data analyst's core function is transforming raw data into actionable insights
through collection, cleaning, analysis, and visualization to guide organizational decision-
making.
2. What does "structured data" refer to?
A) Data stored in unstructured text files B) Data organized into rows and columns within a
defined schema C) Data collected from social media platforms D) Any data that has been
compressed for storage
B) Data organized into rows and columns within a defined schema (correct answer)
Rationale: Structured data conforms to a predefined schema, typically stored in relational
databases with clearly defined rows and columns, making it easily searchable and
analyzable.
,3. Which of the following is an example of unstructured data?
A) A customer database with names and addresses B) A spreadsheet of monthly sales figures C)
An email message or social media post D) A table of employee IDs and salaries
C) An email message or social media post (correct answer)
Rationale: Unstructured data lacks a predefined data model, including text documents,
emails, images, audio, and video — it comprises the majority of data generated today.
4. "Semi-structured data" is best described as:
A) Data with no organizational properties B) Data that has some organizational properties but
does not conform to a rigid schema C) Data that is partially encrypted D) Data stored in half-
normalized database tables
B) Data that has some organizational properties but does not conform to a rigid schema
(correct answer)
Rationale: Semi-structured data (e.g., JSON, XML) uses tags or markers to separate
elements but does not require a fixed schema, offering flexibility between structured and
unstructured formats.
5. Which SQL command is used to retrieve data from a database?
A) INSERT B) UPDATE C) SELECT D) DELETE
C) SELECT (correct answer)
Rationale: The SELECT statement is the foundational SQL query command, allowing
users to retrieve specified columns and rows from one or more database tables.
6. What does the SQL WHERE clause do?
A) Sorts the result set in ascending or descending order B) Filters rows based on a specified
condition C) Groups rows with the same values D) Joins two tables together
B) Filters rows based on a specified condition (correct answer)
,Rationale: The WHERE clause applies row-level filtering to a query, returning only
records that meet the specified condition(s), reducing the dataset to relevant results.
7. Which SQL clause is used to sort query results?
A) GROUP BY B) HAVING C) ORDER BY D) FILTER BY
C) ORDER BY (correct answer)
Rationale: ORDER BY sorts the result set by one or more columns in ascending (ASC,
default) or descending (DESC) order.
8. What is the purpose of the SQL GROUP BY clause?
A) To filter rows before aggregation B) To combine rows with the same values in specified
columns into summary rows C) To join multiple tables D) To eliminate duplicate column names
B) To combine rows with the same values in specified columns into summary rows (correct
answer)
Rationale: GROUP BY collapses multiple rows sharing the same value(s) in specified
columns into a single summary row, enabling aggregate calculations like COUNT, SUM,
and AVG per group.
9. Which SQL clause filters groups after aggregation?
A) WHERE B) HAVING C) GROUP BY D) ORDER BY
B) HAVING (correct answer)
Rationale: HAVING filters grouped results after aggregation — unlike WHERE which
filters individual rows before grouping, HAVING applies conditions to aggregated values
like SUM or COUNT.
10. What does the SQL JOIN operation do?
, A) Combines rows from two or more tables based on a related column B) Removes duplicate
rows from a result set C) Sorts the output by a foreign key D) Creates a new table from existing
data
A) Combines rows from two or more tables based on a related column (correct answer)
Rationale: JOINs merge data from multiple tables using a matching key, enabling queries
that span relationships across the relational database schema.
11. An INNER JOIN returns:
A) All rows from the left table and matching rows from the right B) Only rows where there is a
match in both tables C) All rows from both tables regardless of match D) All rows from the right
table and matching rows from the left
B) Only rows where there is a match in both tables (correct answer)
Rationale: INNER JOIN returns the intersection of two tables — only records where the
join condition is satisfied in both tables are included in the result set.
12. A LEFT (OUTER) JOIN returns:
A) Only matching rows from both tables B) All rows from the left table and matching rows from
the right; NULLs where no match exists C) All rows from the right table only D) All rows from
both tables with no NULLs
B) All rows from the left table and matching rows from the right; NULLs where no match
exists (correct answer)
Rationale: A LEFT JOIN preserves every row from the left (first) table and fills in NULL
values for right-table columns where no matching row exists.
13. What does a FULL OUTER JOIN return?
A) Only matching rows B) All rows from both tables, with NULLs where there is no match on
either side C) All rows from the left table only D) Cartesian product of both tables
B) All rows from both tables, with NULLs where there is no match on either side (correct
answer)
Practice Questions (Data Analytics, SQL, Data
Management & Professional Practice)
These cover SQL fundamentals, data modeling, ETL/warehousing, data quality & governance,
machine learning, statistics, data visualization, privacy/security, NoSQL, big data, and
professional practice — aligned with the D204 course objectives. Good luck on your assessment
1. Which of the following best describes the role of a data analyst?
A) Designing hardware infrastructure for data storage B) Collecting, cleaning, and interpreting
data to support business decisions C) Writing operating system code for database servers D)
Managing network security for cloud platforms
B) Collecting, cleaning, and interpreting data to support business decisions (correct
answer)
Rationale: A data analyst's core function is transforming raw data into actionable insights
through collection, cleaning, analysis, and visualization to guide organizational decision-
making.
2. What does "structured data" refer to?
A) Data stored in unstructured text files B) Data organized into rows and columns within a
defined schema C) Data collected from social media platforms D) Any data that has been
compressed for storage
B) Data organized into rows and columns within a defined schema (correct answer)
Rationale: Structured data conforms to a predefined schema, typically stored in relational
databases with clearly defined rows and columns, making it easily searchable and
analyzable.
,3. Which of the following is an example of unstructured data?
A) A customer database with names and addresses B) A spreadsheet of monthly sales figures C)
An email message or social media post D) A table of employee IDs and salaries
C) An email message or social media post (correct answer)
Rationale: Unstructured data lacks a predefined data model, including text documents,
emails, images, audio, and video — it comprises the majority of data generated today.
4. "Semi-structured data" is best described as:
A) Data with no organizational properties B) Data that has some organizational properties but
does not conform to a rigid schema C) Data that is partially encrypted D) Data stored in half-
normalized database tables
B) Data that has some organizational properties but does not conform to a rigid schema
(correct answer)
Rationale: Semi-structured data (e.g., JSON, XML) uses tags or markers to separate
elements but does not require a fixed schema, offering flexibility between structured and
unstructured formats.
5. Which SQL command is used to retrieve data from a database?
A) INSERT B) UPDATE C) SELECT D) DELETE
C) SELECT (correct answer)
Rationale: The SELECT statement is the foundational SQL query command, allowing
users to retrieve specified columns and rows from one or more database tables.
6. What does the SQL WHERE clause do?
A) Sorts the result set in ascending or descending order B) Filters rows based on a specified
condition C) Groups rows with the same values D) Joins two tables together
B) Filters rows based on a specified condition (correct answer)
,Rationale: The WHERE clause applies row-level filtering to a query, returning only
records that meet the specified condition(s), reducing the dataset to relevant results.
7. Which SQL clause is used to sort query results?
A) GROUP BY B) HAVING C) ORDER BY D) FILTER BY
C) ORDER BY (correct answer)
Rationale: ORDER BY sorts the result set by one or more columns in ascending (ASC,
default) or descending (DESC) order.
8. What is the purpose of the SQL GROUP BY clause?
A) To filter rows before aggregation B) To combine rows with the same values in specified
columns into summary rows C) To join multiple tables D) To eliminate duplicate column names
B) To combine rows with the same values in specified columns into summary rows (correct
answer)
Rationale: GROUP BY collapses multiple rows sharing the same value(s) in specified
columns into a single summary row, enabling aggregate calculations like COUNT, SUM,
and AVG per group.
9. Which SQL clause filters groups after aggregation?
A) WHERE B) HAVING C) GROUP BY D) ORDER BY
B) HAVING (correct answer)
Rationale: HAVING filters grouped results after aggregation — unlike WHERE which
filters individual rows before grouping, HAVING applies conditions to aggregated values
like SUM or COUNT.
10. What does the SQL JOIN operation do?
, A) Combines rows from two or more tables based on a related column B) Removes duplicate
rows from a result set C) Sorts the output by a foreign key D) Creates a new table from existing
data
A) Combines rows from two or more tables based on a related column (correct answer)
Rationale: JOINs merge data from multiple tables using a matching key, enabling queries
that span relationships across the relational database schema.
11. An INNER JOIN returns:
A) All rows from the left table and matching rows from the right B) Only rows where there is a
match in both tables C) All rows from both tables regardless of match D) All rows from the right
table and matching rows from the left
B) Only rows where there is a match in both tables (correct answer)
Rationale: INNER JOIN returns the intersection of two tables — only records where the
join condition is satisfied in both tables are included in the result set.
12. A LEFT (OUTER) JOIN returns:
A) Only matching rows from both tables B) All rows from the left table and matching rows from
the right; NULLs where no match exists C) All rows from the right table only D) All rows from
both tables with no NULLs
B) All rows from the left table and matching rows from the right; NULLs where no match
exists (correct answer)
Rationale: A LEFT JOIN preserves every row from the left (first) table and fills in NULL
values for right-table columns where no matching row exists.
13. What does a FULL OUTER JOIN return?
A) Only matching rows B) All rows from both tables, with NULLs where there is no match on
either side C) All rows from the left table only D) Cartesian product of both tables
B) All rows from both tables, with NULLs where there is no match on either side (correct
answer)
