FC0-U71 Data and Database Fundamentals Practice Question
A database administrator is designing a table to store employee records. She needs to ensure that no two employees can have the same employee number, and that the employee number is never left blank. Which combination of constraints should she apply to the employee number column?
⚠ Common exam trap
The trap here is thinking that an index or AUTO_INCREMENT automatically enforces uniqueness and non-null values, when only explicit constraints guarantee those rules.
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 and NOT NULL
To require that every employee has a unique employee number, the column needs both a uniqueness rule and a non-null rule. UNIQUE prevents duplicates, and NOT NULL prevents blanks. A primary key would also work, but the question asks for a combination of constraints; UNIQUE and NOT NULL are the specific constraints that meet both conditions.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
INDEX and AUTO_INCREMENT
Why it's wrong here
An index speeds up queries but does not enforce uniqueness unless it is a unique index. AUTO_INCREMENT generates sequential numbers but does not by itself prevent duplicates if values are manually inserted. This combination may help with performance and automatic numbering, but it does not guarantee that employee numbers are unique and never blank.
- ✓
UNIQUE and NOT NULL
Why this is correct
The UNIQUE constraint prevents duplicate employee numbers, and the NOT NULL constraint ensures the column cannot be left empty. Together they satisfy both requirements: every employee has an employee number, and no two employees share the same one. This is a standard way to enforce a candidate key when the column is not the table's primary key.
- ✗
PRIMARY KEY and FOREIGN KEY
Why it's wrong here
A primary key already enforces uniqueness and non-null values, so adding a foreign key is unnecessary and would require the employee number to reference another table. A foreign key is used to link to a parent table, not to enforce uniqueness within the employee table. This combination does not match the requirement and could create an inappropriate dependency.
- ✗
CHECK and DEFAULT
Why it's wrong here
A CHECK constraint validates that values meet a condition, such as a range, but it does not automatically prevent duplicates unless a complex condition is written. A DEFAULT supplies a value when none is given, which could actually hide missing data. This combination does not reliably enforce uniqueness and non-null requirements for employee numbers.
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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.