DA0-002 Data Concepts and Environments Practice Question
A data analyst needs to combine customer information from a CRM table and order information from an orders table, returning only customers who have placed at least one order. Which type of join should the analyst use?
⚠ Common exam trap
The CompTIA Data+ exam often tests the misconception that a LEFT JOIN will include only customers with orders because it 'joins' the tables, but the trap is that a LEFT JOIN preserves all rows from the left table, including those with no matches, so it does not filter out customers without orders.
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
✓
INNER JOIN
An INNER JOIN between the CRM table and the orders table returns only rows where there is a match in both tables based on the join key (e.g., customer ID). This satisfies the requirement to return only customers who have placed at least one order, because any customer without an order in the orders table will be excluded from the result set.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
RIGHT JOIN
Why it's wrong here
A RIGHT JOIN returns every row from the orders table plus matching CRM rows, so it preserves orders lacking customers rather than filtering to customers with orders. It is tempting because it does return matched pairs, but it also emits unmatched orders. An INNER JOIN returns only rows where customer and order keys match on both sides.
- ✓
INNER JOIN
Why this is correct
An INNER JOIN returns only rows where the join key matches in both tables, so customers without orders are excluded and only customers with at least one order remain. A LEFT JOIN would retain unmatched customers, contradicting the stated requirement.
- ✗
FULL OUTER JOIN
Why it's wrong here
A FULL OUTER JOIN returns matched rows plus unmatched rows from both tables, so customers without orders and orders without customers both appear. It is tempting because it guarantees no matched pair is lost, but the stem requires excluding customers who never ordered. An INNER JOIN discards those unmatched rows on both sides.
- ✗
LEFT JOIN
Why it's wrong here
A LEFT JOIN returns every CRM customer, including those with no orders, whose order columns appear as NULL. It is tempting because it keeps all customer data, but the stem requires only customers who placed at least one order. An INNER JOIN drops non-ordering customers by requiring matching keys in both tables.
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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.