Quick Answer
The correct answer is to apply both the UNIQUE and NOT NULL constraints to the email column. This is because the UNIQUE constraint ensures that no two customers can share the same email address, preventing duplicate entries, while the NOT NULL constraint guarantees that the email field must always contain a value, satisfying the requirement that an email is always provided. On the CompTIA ITF+ FC0-U61 exam, this scenario tests your understanding of how SQL constraints enforce data integrity at the column level; a common trap is assuming that a PRIMARY KEY alone would suffice, but since the email is not necessarily the table’s primary identifier, the combination of UNIQUE and NOT NULL is the precise tool for a mandatory, distinct column. Remember the mnemonic “UNN” for UNique and Not Null—think of it as a double lock ensuring both uniqueness and completeness.
This FC0-U61 practice question tests your understanding of it concepts and terminology. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A database manager is designing a new table to store customer information for a retail company. The table needs to store a unique identifier for each customer, the customer's first and last name, email address, phone number, and date of birth. The manager also wants to ensure that the email address is always provided and that no two customers have the same email. Which of the following SQL constraints should be applied to the email column?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "first"
Why it matters: Order matters here. You are being tested on which action comes before the others — not which action is generally useful.
Clue: "always"
Why it matters: Absolute qualifier. An answer using 'always' is only correct if there are genuinely no exceptions — absolute statements are often wrong in networking.
INDEX
Why wrong: An index speeds up queries but does not enforce data integrity rules.
FOREIGN KEY
Why wrong: A foreign key references another table; not applicable to email.
PRIMARY KEY
Why wrong: A primary key is often an ID column, not the email, though it could be used, but it's not typical for email.
UNIQUE and NOT NULL
These constraints ensure email is mandatory and distinct.
Answer choices
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
The email column must be both unique (to prevent duplicate email addresses) and NOT NULL (to ensure an email is always provided). The UNIQUE constraint enforces that no two rows have the same value, and NOT NULL guarantees that the column cannot be left empty. Together, they satisfy the requirement that every customer has a distinct, mandatory email address.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
INDEX
Why it's wrong here
An index speeds up queries but does not enforce data integrity rules.
FOREIGN KEY
Why it's wrong here
A foreign key references another table; not applicable to email.
PRIMARY KEY
Why it's wrong here
A primary key is often an ID column, not the email, though it could be used, but it's not typical for email.
UNIQUE and NOT NULL
Why this is correct
These constraints ensure email is mandatory and distinct.
Clue confirmation
The clue words "first", "always" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
The trap here is that candidates confuse PRIMARY KEY with UNIQUE+NOT NULL, not realizing that a table can have only one primary key and that email is often a natural key requiring both uniqueness and mandatory presence, but not necessarily the table's primary identifier.
Detailed technical explanation
Under the hood, a UNIQUE constraint creates a unique index (typically a B-tree) to enforce uniqueness, while NOT NULL is a column-level constraint stored in the table metadata. In SQL, a table can have multiple UNIQUE constraints but only one PRIMARY KEY; combining UNIQUE and NOT NULL on a column effectively makes it a candidate key, which is a common pattern for natural keys like email addresses. In real-world retail systems, this ensures that login or communication systems can rely on email as a stable, non-repeating identifier.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A practitioner preparing for the FC0-U61 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
What to study next
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FAQ
IT Concepts and Terminology — This question tests IT Concepts and Terminology — Read the scenario before looking for a memorised answer..
The correct answer is: UNIQUE and NOT NULL — The email column must be both unique (to prevent duplicate email addresses) and NOT NULL (to ensure an email is always provided). The UNIQUE constraint enforces that no two rows have the same value, and NOT NULL guarantees that the column cannot be left empty. Together, they satisfy the requirement that every customer has a distinct, mandatory email address.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Yes — watch for: "first", "always". Order matters here. You are being tested on which action comes before the others — not which action is generally useful.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 25, 2026
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