Quick Answer
The correct answer is the foreign key constraint. This is because a foreign key constraint enforces referential integrity by ensuring that every patient_id value entered into the visits table must already exist as a valid primary key in the patient table, preventing orphan records or invalid references. On the CompTIA Data+ DA0-001 exam, this concept tests your understanding of how relational databases maintain consistency across linked tables; a common trap is confusing foreign keys with primary keys or unique constraints, which handle uniqueness within a single table rather than cross-table relationships. To remember, think of the foreign key as a "bridge" that connects two tables, ensuring no visit can reference a nonexistent patient. A helpful mnemonic is "FK = Foreign Key = Forges Kinship" between tables, guaranteeing every child record has a valid parent.
This DA0-001 practice question tests your understanding of comparing and contrasting data concepts. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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 healthcare database stores patient records. Each patient has a unique patient_id, and the database includes a table 'visits' with visit_id, patient_id, visit_date, and diagnosis_code. To ensure data integrity, which constraint should be applied to the patient_id column in the 'visits' table?
Unique constraint
Why wrong: Unique constraint prevents duplicate values, not referential integrity.
Foreign key
Foreign key enforces referential integrity.
Primary key
Why wrong: Primary key is for the table's own unique identifier.
Check constraint
Why wrong: Check constraint validates data range or format.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Foreign key
Option B is correct because a foreign key constraint ensures that patient_id in visits references a valid patient_id in the patient table. Option A is wrong because primary key ensures uniqueness in its own table. Option C is wrong because unique constraint prevents duplicates. Option D is wrong because check constraint validates values based on a condition.
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
Unique constraint
Why it's wrong here
Unique constraint prevents duplicate values, not referential integrity.
Foreign key
Why this is correct
Foreign key enforces referential integrity.
Related concept
Static NAT maps one inside address to one outside address.
Primary key
Why it's wrong here
Primary key is for the table's own unique identifier.
Check constraint
Why it's wrong here
Check constraint validates data range or format.
Common exam traps
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Detailed technical explanation
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Real-world example
A small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
What to study next
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related DA0-001 NAT questions on configuration and troubleshooting.
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FAQ
Comparing and Contrasting Data Concepts — This question tests Comparing and Contrasting Data Concepts — Static NAT maps one inside address to one outside address..
The correct answer is: Foreign key — Option B is correct because a foreign key constraint ensures that patient_id in visits references a valid patient_id in the patient table. Option A is wrong because primary key ensures uniqueness in its own table. Option C is wrong because unique constraint prevents duplicates. Option D is wrong because check constraint validates values based on a condition.
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related DA0-001 NAT questions on configuration and troubleshooting.
Static NAT maps one inside address to one outside address.
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Last reviewed: Jun 6, 2026
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