Quick Answer
The answer is LEFT JOIN. This is the correct choice because a LEFT JOIN ensures you keep all rows from the left table—in this case, the Orders table—while pulling in matching data from the right table, Customers. When no match exists, the query returns NULL values for the customer columns, perfectly satisfying the requirement to include every order regardless of whether a customer record is present. On the CompTIA Data+ DA0-001 exam, this question tests your understanding of join types and their real-world application in data analysis; a common trap is confusing LEFT JOIN with INNER JOIN, which would drop orders without matching customers. To remember, think of the keyword “LEFT” as meaning “leave everything on the left side intact.” A simple memory tip: visualize the left table as the boss—it always keeps its full team, even if the right table has no one to pair with them.
This DA0-001 practice question tests your understanding of analyzing and modeling data. 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 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?
RIGHT JOIN
Why wrong: RIGHT JOIN returns all customers, which could ignore orders without customer match.
FULL OUTER JOIN
Why wrong: FULL OUTER JOIN returns all rows from both tables, but not needed if only all orders are required.
LEFT JOIN
LEFT JOIN returns all orders, including those without matching customers.
INNER JOIN
Why wrong: INNER JOIN only returns rows with matching customer records, omitting unmatched orders.
Answer choices
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.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
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.
Related concept
Read the scenario before looking for a memorised answer.
INNER JOIN
Why it's wrong here
INNER JOIN only returns rows with matching customer records, omitting unmatched orders.
Common exam traps
The trap here is that candidates often 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.
Detailed technical explanation
Under the hood, a LEFT JOIN performs a nested-loop or hash join, preserving the left table's rows and probing the right table for matches. In a real-world scenario, this is critical for reporting on orphaned orders (e.g., deleted customer accounts) to ensure revenue data is not lost. A subtle behavior: if the right table has multiple matching rows, the LEFT JOIN will duplicate the left row for each match, which can inflate row counts unexpectedly.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A practitioner preparing for the DA0-001 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
What to study next
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FAQ
Analyzing and Modeling Data — This question tests Analyzing and Modeling Data — Read the scenario before looking for a memorised answer..
The correct answer is: 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.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 24, 2026
This DA0-001 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 DA0-001 exam.
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