Question 1mediummultiple choice
Full question →mediummultiple choiceObjective-mapped
A development team is designing a relational database for a hospital patient management system. They need to ensure that each patient's medical record number is unique and not null. Which database constraint should they use?
Answer choices
Why each option matters
Good practice is not just finding the correct option. The wrong answers often show the exact trap the exam wants you to fall into.
A
Distractor review
FOREIGN KEY
Incorrect. FOREIGN KEY constraints are used to enforce relationships between tables, not to ensure uniqueness or non-null on a single column.
B
Distractor review
CHECK
Incorrect. CHECK constraints validate that data meets a Boolean expression, but they do not inherently enforce uniqueness.
C
Distractor review
UNIQUE
Incorrect. A UNIQUE constraint guarantees uniqueness but allows one null value in most database systems. The requirement specifies non-null as well.
D
Best answer
PRIMARY KEY
Correct. A PRIMARY KEY constraint enforces both uniqueness and non-null, making it ideal for the medical record number.
Common exam trap
Common exam trap: NAT rules depend on direction and matching traffic
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.
Technical deep dive
How to think about this question
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.
KKey Concepts to Remember
- Static NAT maps one inside address to one outside address.
- PAT allows many inside hosts to share one public address using ports.
- Inside local and inside global describe the private and translated addresses.
- NAT ACLs identify traffic for translation, not always security filtering.
TExam Day Tips
- Identify inside and outside interfaces first.
- Check whether the scenario needs static NAT, dynamic NAT or PAT.
- Do not confuse NAT matching ACLs with normal packet-filtering intent.
Related practice questions
Related DP-900 practice-question pages
Use these pages to review the topic behind this question. This is how one missed question becomes focused revision.
More questions from this exam
Keep practising from the same exam bank, or move into a focused topic page if this question exposed a weak area.
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FAQ
Questions learners often ask
What does this DP-900 question test?
Static NAT maps one inside address to one outside address.
What is the correct answer to this question?
The correct answer is: PRIMARY KEY — A PRIMARY KEY constraint enforces both uniqueness and non-null on a column or set of columns. A FOREIGN KEY maintains referential integrity between tables. A CHECK constraint enforces custom rules (e.g., age > 0). A UNIQUE constraint ensures uniqueness but allows null values (unless specified otherwise). Therefore, PRIMARY KEY is the appropriate choice.
What should I do if I get this DP-900 question wrong?
Then try more questions from the same exam bank and focus on understanding why the wrong options are tempting.
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