To answer this question, you need to understand the purpose of a FULL OUTER JOIN.
A FULL OUTER JOIN returns all records from both tables, including matched and unmatched data. It combines the results of both LEFT JOIN and RIGHT JOIN.
Let's go through each option to understand why it is correct or incorrect:
Option A) Both tables have NULL values - This option is not a specific condition for using a FULL OUTER JOIN. A FULL OUTER JOIN can be used even if both tables do not have NULL values.
Option B) You want all unmatched data from one table - This option is not a specific condition for using a FULL OUTER JOIN. A FULL OUTER JOIN returns all unmatched data from both tables.
Option C) You want all matched data from both tables - This option is not correct. A FULL OUTER JOIN returns all matched and unmatched data from both tables.
Option D) You want all unmatched data from both tables - This option is correct. A FULL OUTER JOIN returns all unmatched data from both tables.
Option E) One of the tables has more data than the other - This option is not a specific condition for using a FULL OUTER JOIN. A FULL OUTER JOIN can be used regardless of the size of the tables.
Option F) You want all matched and unmatched data from only one table - This option is not correct. A FULL OUTER JOIN returns all matched and unmatched data from both tables.
The correct answer is option D. This option is correct because a FULL OUTER JOIN is used when you want to retrieve all unmatched data from both tables.