easyMultiple ChoiceObjective-mapped
FC0-U71 Practice Question: A database designer wants to ensure that no two…
A database designer wants to ensure that no two employees have the same email address. Which constraint should be applied to the Email column?
⚠ Common exam trap
A common mix-up: candidates 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.
Answer choices
Why each option matters
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.
Answer analysis
Option-by-option breakdown
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.
- ✗
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.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This FC0-U71 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-U71 exam.