→ FULL OUTER JOIN returns all rows from both tables, inserting NULLs where no match exists. This join includes the maximum possible number of records — all matches, plus all unmatched records from both sides.
Why the other options are incorrect:
A: INNER JOIN returns only matching rows — less total data.
B & C: LEFT/RIGHT JOIN include all rows from one table only.
Official References:
CompTIA DataX (DY0-001) Study Guide – Section 5.2:“A FULL OUTER JOIN maximizes data volume by including all matched and unmatched records from both tables.”
SQL for Data Science, Chapter 4:“Use FULL OUTER JOIN when the goal is to preserve every record from both datasets regardless of match.”
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