AI0-001 AI Models and Data Engineering Practice Question
A data engineer needs to combine two datasets, each with unique customer_id, to include all records from both datasets. Which join type should be used?
⚠ Common exam trap
CompTIA often tests the misconception that LEFT JOIN or RIGHT JOIN can include all records from both datasets, but candidates forget that these asymmetric joins exclude non-matching rows from the opposite side.
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
✓
FULL OUTER JOIN
A FULL OUTER JOIN returns all records from both datasets, matching rows where the customer_id is present in both and filling in NULLs for missing matches. This is the only join type that guarantees every unique customer_id from either dataset appears in the result, which is exactly what the requirement specifies.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
FULL OUTER JOIN
Why this is correct
FULL OUTER JOIN includes all records from both tables, matching where possible and filling nulls elsewhere.
- ✗
RIGHT JOIN
Why it's wrong here
RIGHT JOIN returns all rows from the right table, but may miss unmatched rows from the left.
- ✗
LEFT JOIN
Why it's wrong here
LEFT JOIN returns all rows from the left table, but may miss unmatched rows from the right.
- ✗
INNER JOIN
Why it's wrong here
INNER JOIN only returns rows with matching keys in both tables, excluding unmatched records.
About these practice questions
Courseiva writes every AI0-001 question from scratch — 754 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 by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This AI0-001 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 AI0-001 exam.