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FC0-U71 Practice Question: A database designer is creating a table to store…
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?
⚠ Common exam trap
Many candidates 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.
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
✓
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.
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 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.
- ✗
NOT NULL
Why it's wrong here
NOT NULL prevents null values but does not enforce 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.