Quick Answer
The correct choice is the UNIQUE constraint because it enforces unique column values across all rows in a table, ensuring that no two employees can share the same email address. This constraint guarantees that every entry in the Email column is distinct, directly implementing the business rule of unique email addresses without requiring the column to serve as the table’s primary key. On the CompTIA ITF+ FC0-U61 exam, this concept tests your understanding of how UNIQUE differs from PRIMARY KEY—a common trap is assuming only PRIMARY KEY can enforce uniqueness, but UNIQUE allows one NULL value (though email columns are typically set to NOT NULL in practice). The exam often presents scenarios like employee IDs or usernames where you must choose between these two constraints. A solid memory tip: think of UNIQUE as a “bouncer” that lets in only one of each value, but it can leave the door slightly ajar for a single NULL.
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 wants to ensure that no two employees have the same email address. Which constraint should be applied to the Email column?
UNIQUE
UNIQUE constraint ensures no duplicate email addresses.
PRIMARY KEY
Why wrong: PRIMARY KEY forces uniqueness and non-null, but is usually applied to the employee ID, not email.
CHECK
Why wrong: CHECK constraint validates data based on a condition, but does not prevent duplicates.
FOREIGN KEY
Why wrong: FOREIGN KEY links tables and enforces referential integrity, not 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
UNIQUE
The UNIQUE constraint ensures that all values in the Email column are distinct, preventing any two employees from having the same email address. Unlike PRIMARY KEY, UNIQUE allows NULL values (though typically email columns are set to NOT NULL), and it can be applied to non-key columns. This directly enforces the business rule of unique email addresses without requiring the column to be the table's primary identifier.
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 this is correct
UNIQUE constraint ensures no duplicate email addresses.
Related concept
Read the scenario before looking for a memorised answer.
PRIMARY KEY
Why it's wrong here
PRIMARY KEY forces uniqueness and non-null, but is usually applied to the employee ID, not email.
CHECK
Why it's wrong here
CHECK constraint validates data based on a condition, but does not prevent duplicates.
FOREIGN KEY
Why it's wrong here
FOREIGN KEY links tables and enforces referential integrity, not uniqueness.
Common exam traps
The trap here is that candidates often confuse UNIQUE with PRIMARY KEY, assuming uniqueness can only be enforced by a primary key, but PRIMARY KEY imposes additional non-null and single-per-table restrictions that are not required for simply ensuring unique email addresses.
Detailed technical explanation
Under the hood, a UNIQUE constraint creates a non-clustered index (in SQL Server) or a unique index (in MySQL, PostgreSQL) on the column, which the database engine uses to check for duplicates on every INSERT or UPDATE. In real-world scenarios, a UNIQUE constraint on an email column is critical for preventing duplicate user accounts, and it can be combined with a CHECK constraint to validate email format (e.g., CHECK (Email LIKE '%@%.%')). Note that in some databases, multiple NULL values are allowed under a UNIQUE constraint (e.g., SQL Server, PostgreSQL), but MySQL treats NULLs as distinct values, allowing multiple NULLs.
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
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Database Fundamentals — study guide chapter
Learn the concepts, then practise the questions
Database Fundamentals practice questions
Targeted practice on this topic area only
All FC0-U61 questions
512 questions across all exam domains
CompTIA ITF+ FC0-U61 study guide
Full concept coverage aligned to exam objectives
FC0-U61 practice test guide
How to use practice tests most effectively before exam day
Related practice questions
Use these pages to review the topic behind this question. This is how one missed question becomes focused revision.
Practise FC0-U61 questions linked to IT Concepts and Terminology.
Practise FC0-U61 questions linked to Infrastructure.
Practise FC0-U61 questions linked to Applications and Software.
Practise FC0-U61 questions linked to Software Development Concepts.
Practise FC0-U61 questions linked to Security.
Practise FC0-U61 questions linked to Database Fundamentals.
Practise FC0-U61 questions linked to FC0-U61 fundamentals.
Practise FC0-U61 questions linked to FC0-U61 scenario.
Practise FC0-U61 questions linked to FC0-U61 troubleshooting.
Practice this exam
Short sessions build daily habit. Longer sessions build exam-day stamina. Try a timed session to simulate real conditions.
FAQ
Database Fundamentals — This question tests Database Fundamentals — Read the scenario before looking for a memorised answer..
The correct answer is: UNIQUE — The UNIQUE constraint ensures that all values in the Email column are distinct, preventing any two employees from having the same email address. Unlike PRIMARY KEY, UNIQUE allows NULL values (though typically email columns are set to NOT NULL), and it can be applied to non-key columns. This directly enforces the business rule of unique email addresses without requiring the column to be the table's primary identifier.
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.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Last reviewed: Jun 11, 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.
Question Discussion
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
Sign in to join the discussion.