DA0-002 Data Concepts and Environments Practice Question
A table named Orders has columns OrderID, CustomerID, OrderDate, and TotalAmount. Which column should be the primary key to uniquely identify each order?
⚠ Common exam trap
Test-takers frequently confuse a column that is frequently used for filtering or grouping (like CustomerID or OrderDate) with one that guarantees uniqueness, overlooking the fundamental primary key requirement of uniqueness and non-nullability.
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
✓
OrderID
The OrderID column is the correct choice for the primary key because it contains unique values for each order, ensuring that each row can be uniquely identified. A primary key must be unique, non-null, and stable; OrderID satisfies all these requirements, whereas the other columns do not guarantee uniqueness or are subject to change.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
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OrderDate
Why it's wrong here
OrderDate stores a date shared by many orders, so it cannot uniquely identify each row. It tempts because dates are frequently indexed and queried, but indexing is not uniqueness; OrderID is the column that uniquely identifies each order and belongs as the primary key.
- ✓
OrderID
Why this is correct
OrderID is a surrogate identifier assigned one distinct value per order row, so it guarantees uniqueness and rejects nulls, satisfying the requirement to identify each order individually. CustomerID repeats across a customer's orders, OrderDate collides on same-day purchases, and TotalAmount duplicates readily, so none can enforce entity integrity as the primary key.
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TotalAmount
Why it's wrong here
TotalAmount cannot be a primary key because multiple orders can share identical monetary values, so it does not guarantee uniqueness. It is tempting because it appears distinctive per row, but its actual purpose is aggregation and financial reporting, where duplicate totals are expected and acceptable.
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CustomerID
Why it's wrong here
CustomerID repeats across orders placed by the same customer, so it cannot uniquely identify a row. It tempts as a foreign key linking to the Customers table, which is its actual purpose; OrderID is the column guaranteed unique per order and therefore the primary key.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This DA0-002 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 DA0-002 exam.