WGU D427 Data Management Applications OA Exam [150 Actual Questions] Well-Elaborated & Verified Answers

WGU D427 Data Management Applications OA
Exam [150 Actual Questions] Well-Elaborated &
Verified Answers



Question 1: Which SQL clause is used to remove duplicate rows from a result set in PostgreSQL?


A) DISTINCT


B) UNIQUE


C) NO DUPLICATE


D) SORTED


Correct Answer: A) DISTINCT


Explanation: DISTINCT eliminates duplicate rows; UNIQUE is a constraint, not a clause.


Question 2: A table has a composite primary key (dept_id, emp_num). Which statement is true?


A) Either column may contain nulls


B) Neither column may contain nulls


C) Only dept_id may contain nulls

,D) Only emp_num may contain nulls


Correct Answer: B) Neither column may contain nulls


Explanation: Primary-key columns must be NOT NULL to guarantee uniqueness.


Question 3: Which index type is best for low-cardinality, highly skewed categorical columns in
PostgreSQL?


A) B-tree


B) Hash


C) Bitmap


D) GiST


Correct Answer: C) Bitmap


Explanation: Bitmap indexes compress duplicate values and are optimized for low-cardinality,
skewed data.


Question 4: Which backup format created by pg_dump is compressed and restore-selective?


A) SQL


B) Tar


C) Custom (.dump)


D) Directory

,Correct Answer: C) Custom (.dump)


Explanation: Custom format is binary, compressed, and allows selective restore via pg_restore.


Question 5: Which normal form eliminates transitive dependencies?


A) 1NF


B) 2NF


C) 3NF


D) BCNF


Correct Answer: C) 3NF


Explanation: Third normal form requires that non-key attributes depend only on the key (no
transitive dependency).


Question 6: Which isolation level prevents non-repeatable reads but allows phantom reads?


A) Read uncommitted


B) Read committed


C) Repeatable read


D) Serializable


Correct Answer: C) Repeatable read

, Explanation: Repeatable read ensures rows read twice return the same values, but new rows can
be inserted (phantoms).


Question 7: Which constraint ensures every value in a column comes from a defined set?


A) CHECK


B) UNIQUE


C) PRIMARY KEY


D) FOREIGN KEY


Correct Answer: A) CHECK


Explanation: CHECK enforces domain integrity by limiting values to a Boolean expression.


Question 8) Which ETL phase includes data cleansing and deduplication?


A) Extract


B) Transform


C) Load


D) Validate


Correct Answer: B) Transform


Explanation: Transformation is where cleaning, deduplication, formatting, and business-rule
application occur.