hardMultiple ChoiceObjective-mapped
FC0-U71 Practice Question: A database manager is designing a new table to…
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?
⚠ Common exam trap
It's easy for candidates to 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.
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
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.
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
Why it's wrong here
An index speeds up queries but does not enforce data integrity rules.
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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.
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