DA0-002 Data Analysis Practice Question
A data analyst needs to join two tables in a SQL database: Orders and Customers. The analyst wants to include all orders, even if there is no matching customer record. Which type of join should be used?
⚠ Common exam trap
Test-takers frequently confuse LEFT JOIN with RIGHT JOIN, mistakenly thinking they need to 'keep all customers' instead of 'keep all orders,' or they overcomplicate the requirement by choosing FULL OUTER JOIN when only one side needs to be preserved.
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
✓
LEFT JOIN
A LEFT JOIN returns all rows from the left table (Orders) and the matching rows from the right table (Customers). If there is no match, NULL values are returned for the right table's columns. This satisfies the requirement to include all orders, even those without a matching customer record.
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
RIGHT JOIN returns all customers, which could ignore orders without customer match.
- ✗
FULL OUTER JOIN
Why it's wrong here
FULL OUTER JOIN returns all rows from both tables, but not needed if only all orders are required.
- ✓
LEFT JOIN
Why this is correct
LEFT JOIN returns all orders, including those without matching customers.
- ✗
INNER JOIN
Why it's wrong here
INNER JOIN only returns rows with matching customer records, omitting unmatched orders.
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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.