FC0-U71 Data and Database Fundamentals Practice Question
A database administrator needs to ensure that every record in the 'Orders' table can be uniquely identified. Which constraint should be applied to the 'OrderID' column?
⚠ Common exam trap
The trap is confusing UNIQUE with PRIMARY KEY; candidates pick UNIQUE because it also enforces uniqueness, but they forget that a primary key additionally enforces NOT NULL and serves as the table's official row identifier.
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 table and implicitly enforces uniqueness and NOT NULL. Applying it to OrderID guarantees every order has a unique, non-null identifier, which is exactly what the DBA needs.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
PRIMARY KEY
Why this is correct
A PRIMARY KEY constraint enforces uniqueness and non-nullability on OrderID, guaranteeing each Orders row is uniquely identifiable. Unique constraints permit one null, and foreign keys reference other tables rather than identifying rows, so neither meets the stated requirement.
- ✗
FOREIGN KEY
Why it's wrong here
A foreign key enforces referential integrity between tables, so it cannot guarantee uniqueness within the Orders table itself. It is tempting because it does link records across tables, and it would be the right choice when OrderID values must match existing rows in a parent table, such as linking orders to customers.
- ✗
UNIQUE constraint
Why it's wrong here
A UNIQUE constraint permits one NULL and, crucially, does not guarantee a single designated identifier per row; a table may hold several UNIQUE columns, so it cannot enforce the one primary identifier the scenario demands. It is tempting because UNIQUE suits secondary columns such as email addresses, where duplicates must be blocked but the column is not the table's primary identifier.
- ✗
CHECK constraint
Why it's wrong here
A CHECK constraint enforces a Boolean condition on column values; it does not guarantee uniqueness. It is tempting because it is a column-level constraint, but it would be correct for validating data ranges or formats, whereas a PRIMARY KEY or UNIQUE constraint provides the unique identification of each record.
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Same concept, more angles
1 more way this is tested on FC0-U71
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A company needs to store customer orders and ensure that each order is uniquely identified. Which database concept should be used?
easy- A.Constraint
- B.Index
- C.Foreign key
- ✓ D.Primary key
Why D: A primary key is a column (or set of columns) that uniquely identifies each row in a table, which is exactly what is needed to ensure each customer order has a unique identifier. Primary keys enforce uniqueness and cannot contain NULL values, guaranteeing every order record is distinguishable.
JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official CompTIA exam blueprint
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.