Quick Answer
The answer is the PRIMARY KEY constraint. This is the correct choice because a primary key enforces both uniqueness and non-nullability, meaning it guarantees that every record in a table—such as each employee row—can be uniquely identified by a value that is never blank and never duplicated. On the CompTIA ITF+ FC0-U61 exam, this concept tests your understanding of fundamental database design, often appearing in scenario-based questions where you must choose the constraint that ensures row-level identity. A common trap is confusing PRIMARY KEY with UNIQUE: while both prevent duplicates, only PRIMARY KEY also forbids NULL values, making it the definitive identifier for a table. To remember, think of a primary key as a social security number—every person has exactly one, and it can never be missing or shared.
This FC0-U61 practice question tests your understanding of database fundamentals. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A database designer is creating a table to store employee information. To ensure that each employee can be uniquely identified, which constraint should be applied?
UNIQUE
Why wrong: A unique constraint ensures uniqueness but allows NULL values; primary key is the standard unique identifier.
FOREIGN KEY
Why wrong: A foreign key links tables but does not ensure uniqueness within the table.
PRIMARY KEY
A primary key uniquely identifies each row and cannot contain NULL.
NOT NULL
Why wrong: NOT NULL prevents null values but does not enforce uniqueness.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
PRIMARY KEY
A PRIMARY KEY constraint uniquely identifies each record in a database table. It enforces both uniqueness and non-nullability, ensuring that no two employees can have the same primary key value and that the value is never NULL. This makes it the correct choice for guaranteeing each employee can be uniquely identified.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
UNIQUE
Why it's wrong here
A unique constraint ensures uniqueness but allows NULL values; primary key is the standard unique identifier.
FOREIGN KEY
Why it's wrong here
A foreign key links tables but does not ensure uniqueness within the table.
PRIMARY KEY
Why this is correct
A primary key uniquely identifies each row and cannot contain NULL.
Related concept
Read the scenario before looking for a memorised answer.
NOT NULL
Why it's wrong here
NOT NULL prevents null values but does not enforce uniqueness.
Common exam traps
The trap here is that candidates often confuse UNIQUE with PRIMARY KEY, not realizing that UNIQUE allows a NULL value (which cannot serve as a guaranteed identifier) and that PRIMARY KEY inherently includes both uniqueness and non-nullability.
Detailed technical explanation
Under the hood, a PRIMARY KEY automatically creates a unique clustered index (in SQL Server) or a unique index (in MySQL/PostgreSQL) on the column(s), which physically organizes the data for fast lookup. In a real-world HR system, the EmployeeID column would be set as the PRIMARY KEY, ensuring that even if two employees share the same name, they are distinguished by their unique ID. A subtle behavior is that a table can have only one PRIMARY KEY, but it can be composite (multiple columns), whereas multiple UNIQUE constraints are allowed.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A practitioner preparing for the FC0-U61 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
What to study next
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FAQ
Database Fundamentals — This question tests Database Fundamentals — Read the scenario before looking for a memorised answer..
The correct answer is: PRIMARY KEY — A PRIMARY KEY constraint uniquely identifies each record in a database table. It enforces both uniqueness and non-nullability, ensuring that no two employees can have the same primary key value and that the value is never NULL. This makes it the correct choice for guaranteeing each employee can be uniquely identified.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 25, 2026
This FC0-U61 practice question is part of Courseiva's free CompTIA certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the FC0-U61 exam.
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