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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
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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.
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UNIQUE
Why it's wrong here
UNIQUE enforces distinct values within a column but typically permits multiple NULLs and, unlike a primary key, does not itself designate the row's identifying column. It suits secondary attributes such as email addresses, where duplicates must be blocked but the column is not the table's primary identifier.
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FOREIGN KEY
Why it's wrong here
A FOREIGN KEY constrains values to match rows in a referenced table, enforcing referential integrity between tables rather than uniqueness within this one. It is the right choice when linking employees to a departments table, but it cannot uniquely identify each employee row.
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PRIMARY KEY
Why this is correct
A PRIMARY KEY enforces uniqueness and implicitly rejects NULLs, guaranteeing every employee row has a distinct identifier. This directly satisfies the stem's requirement that each employee be uniquely identified, unlike UNIQUE alone, which permits NULLs and therefore cannot guarantee identification.
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NOT NULL
Why it's wrong here
NOT NULL only forbids null values in a column; it permits duplicate entries, so two employees could share the same identifier. It is used to enforce mandatory data entry, such as requiring every employee record to have a surname, not to guarantee uniqueness across rows.
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JA
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.