FC0-U71 Data and Database Fundamentals Practice Question
A small business is setting up a database to track its customers and their orders. The owner wants to ensure that every order is linked to an existing customer and that the customer ID in the Order table cannot refer to a non-existent customer. Which database concept should be implemented?
⚠ Common exam trap
Watch out — candidates often confuse a primary key with a foreign key; a primary key ensures uniqueness within its own table, while a foreign key enforces referential integrity across tables.
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
✓
Foreign key constraint on the Order table
The requirement is to enforce that every order is linked to a valid customer, which is referential integrity. A foreign key constraint on the Order table referencing the Customer table's primary key ensures that any customer ID entered in the Order table must already exist in the Customer table. This prevents orphaned orders and maintains consistent relationships between the two tables.
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 constraint on the Customer table
Why it's wrong here
A primary key on the Customer table ensures each customer row is unique, but it does not enforce that order records reference valid customers. The requirement is to prevent orders from pointing to non-existent customers, which is a referential integrity concern. A primary key alone does not restrict values in the Order table, so it fails to meet the business rule.
- ✗
Check constraint on the Order table
Why it's wrong here
A check constraint validates that data in a column meets a specific condition, such as OrderAmount > 0. It cannot verify that a customer ID exists in another table. The requirement is to ensure orders reference existing customers, which requires a foreign key relationship, not a check constraint on a single table.
- ✗
Unique constraint on the Order table
Why it's wrong here
A unique constraint on the Order table would ensure that certain columns, such as OrderID, have no duplicate values. However, it does not validate that the customer ID exists in the Customer table. The scenario requires linking orders to valid customers, which is about referential integrity, not uniqueness within the Order table.
- ✓
Foreign key constraint on the Order table
Why this is correct
A foreign key constraint on the Order table references the primary key of the Customer table, ensuring every order's customer ID matches an existing customer. This enforces referential integrity, directly satisfying the requirement that orders cannot be linked to non-existent customers. It prevents orphaned records and maintains consistent relationships between the two tables.
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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.