To answer this question, you need to understand the concept of subqueries in SQL.
A subquery is a query that is nested inside another query. It can be used to retrieve data based on an unknown condition, which makes option D the correct answer.
Let's go through each option to understand why it is correct or incorrect:
Option A) Create groups of data - This option is incorrect because creating groups of data is typically done using the GROUP BY clause, not a subquery.
Option B) Sort data in a specific order - This option is incorrect because sorting data is typically done using the ORDER BY clause, not a subquery.
Option C) Convert data to a different format - This option is incorrect because converting data to a different format is typically done using functions like CAST or CONVERT, not a subquery.
Option D) Retrieve data based on an unknown condition - This option is correct because a subquery can be used to retrieve data based on an unknown condition. The subquery can be used within the WHERE clause to filter the data based on a condition that is dynamically determined.
Therefore, the correct answer is D.