DA0-002 Data Concepts and Environments Practice Question
A data analyst needs to combine rows from two tables based on a related column, but only wants rows that have matching values in both tables. Which join type should the analyst use?
⚠ Common exam trap
DA0-002 often tests the difference between INNER JOIN (matches only) and OUTER JOINs (include unmatched rows with NULLs), so candidates who default to LEFT JOIN for 'combining tables' pick the wrong answer.
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 returns only the rows where the join key exists in both tables, which is exactly what the analyst needs when they want matched records only. Rows with no counterpart in either table are excluded from the result set. This is the default and most common join type in SQL.
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 all rows from the right table plus matched left rows, so unmatched right rows appear with nulls, violating the requirement for matches in both tables. It is tempting because it does combine related columns, and would be correct when every right-table row must be preserved.
- ✓
INNER JOIN
Why this is correct
An INNER JOIN returns only rows where the join key exists in both tables, discarding unmatched rows from either side. This directly satisfies the requirement for rows with matching values in both tables, unlike outer joins that retain unmatched rows.
- ✗
FULL OUTER JOIN
Why it's wrong here
A FULL OUTER JOIN returns all rows from both tables, including non-matching rows with NULLs where no match exists, which violates the requirement to retain only rows with matching values. It is tempting because it does combine rows based on a related column, and would be correct if the analyst needed to preserve unmatched rows from both sides for a complete dataset audit.
- ✗
LEFT JOIN
Why it's wrong here
A LEFT JOIN preserves all rows from the left table, emitting nulls where no right-side match exists, so unmatched rows survive contrary to the requirement. It is tempting because it combines rows on a related column, and would be correct when every left-table row must be retained regardless of matches.
About these practice questions
Courseiva writes every DA0-002 question from scratch — 1,004 in total, each with an explanation and a wrong-answer breakdown. None are copied from real exams or dumps. Learn why practice questions differ from exam dumps →
JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official CompTIA exam blueprint
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.